drivers: some improvements to the ADC driver IF
drivers: some improvements to the ADC driver IF

- removed UNDEFINED value from device enum
- added pre-defined precision values
- added power[on|off] functions
- some minor doxygen fixes

kaleb-himes/RIOT,JensErdmann/RIOT,rfswarm/RIOT,Lotterleben/RIOT,Yonezawa-T2/RIOT,Lexandro92/RIOT-CoAP,kYc0o/RIOT,rfswarm2/RIOT,abkam07/RIOT,LudwigOrtmann/RIOT,changbiao/RIOT,fnack/RIOT,attdona/RIOT,l3nko/RIOT,haoyangyu/RIOT,authmillenon/RIOT,tfar/RIOT,ant9000/RIOT,asanka-code/RIOT,daniel-k/RIOT,luciotorre/RIOT,abkam07/RIOT,sgso/RIOT,plushvoxel/RIOT,Osblouf/RIOT,gbarnett/RIOT,lazytech-org/RIOT,kaspar030/RIOT,plushvoxel/RIOT,malosek/RIOT,thiagohd/RIOT,haoyangyu/RIOT,daniel-k/RIOT,asanka-code/RIOT,AnonMall/RIOT,ks156/RIOT,bartfaizoltan/RIOT,sumanpanchal/RIOT,beurdouche/RIOT,kb2ma/RIOT,neumodisch/RIOT,AnonMall/RIOT,mtausig/RIOT,toonst/RIOT,adjih/RIOT,mtausig/RIOT,fnack/RIOT,toonst/RIOT,shady33/RIOT,FrancescoErmini/RIOT,herrfz/RIOT,jhollister/RIOT,arvindpdmn/RIOT,Yonezawa-T2/RIOT,roberthartung/RIOT,altairpearl/RIOT,mtausig/RIOT,MohmadAyman/RIOT,roberthartung/RIOT,robixnai/RIOT,watr-li/RIOT,AnonMall/RIOT,kaleb-himes/RIOT,beurdouche/RIOT,automote/RIOT,sgso/RIOT,asanka-code/RIOT,Ell-i/RIOT,ks156/RIOT,rfswarm2/RIOT,herrfz/RIOT-old,arvindpdmn/RIOT,bartfaizoltan/RIOT,JensErdmann/RIOT,BytesGalore/RIOT,rakendrathapa/RIOT,neiljay/RIOT,authmillenon/RIOT,watr-li/RIOT,fnack/RIOT,RBartz/RIOT,rfswarm2/RIOT,kaleb-himes/RIOT,dhruvvyas90/RIOT,Yonezawa-T2/RIOT,wentaoshang/RIOT,nsol-nmsu/RIOT,PSHIVANI/Riot-Code,ant9000/RIOT,rousselk/RIOT,1blankz7/RIOT,shady33/RIOT,syin2/RIOT,ant9000/RIOT,RIOT-OS/RIOT,luciotorre/RIOT,herrfz/RIOT-old,avmelnikoff/RIOT,mziegert/RIOT,kYc0o/RIOT,biboc/RIOT,marcosalm/RIOT,EmuxEvans/RIOT,abp719/RIOT,lebrush/RIOT,binarylemon/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,Darredevil/RIOT,benoit-canet/RIOT,kerneltask/RIOT,Osblouf/RIOT,luciotorre/RIOT,lebrush/RIOT,stevenj/RIOT,hamilton-mote/RIOT-OS,DipSwitch/RIOT,rousselk/RIOT,chris-wood/RIOT,msolters/RIOT,lazytech-org/RIOT,chris-wood/RIOT,tfar/RIOT,yogo1212/RIOT,lebrush/RIOT,sgso/RIOT,patkan/RIOT,jferreir/RIOT,beurdouche/RIOT,abp719/RIOT,dailab/RIOT,kaspar030/RIOT,tdautc19841202/RIOT,daniel-k/RIOT,haoyangyu/RIOT,shady33/RIOT,luciotorre/RIOT,jfischer-phytec-iot/RIOT,gautric/RIOT,jasonatran/RIOT,stevenj/RIOT,EmuxEvans/RIOT,ks156/RIOT,MonsterCode8000/RIOT,Lexandro92/RIOT-CoAP,EmuxEvans/RIOT,roberthartung/RIOT,ros2/ros2_embedded_riot,sumanpanchal/RIOT,zhuoshuguo/RIOT,zhuoshuguo/RIOT,abp719/RIOT,biboc/RIOT,openkosmosorg/RIOT,smlng/RIOT,d00616/RIOT,marcosalm/RIOT,stevenj/RIOT,immesys/RiSyn,kushalsingh007/RIOT,ant9000/RIOT,chris-wood/RIOT,kYc0o/RIOT,adrianghc/RIOT,automote/RIOT,rfuentess/RIOT,PSHIVANI/Riot-Code,josephnoir/RIOT,jferreir/RIOT,katezilla/RIOT,Hyungsin/RIOT-OS,ximus/RIOT,Lexandro92/RIOT-CoAP,phiros/RIOT,1blankz7/RIOT,lazytech-org/RIOT,jfischer-phytec-iot/RIOT,josephnoir/RIOT,jhollister/RIOT,shady33/RIOT,benoit-canet/RIOT,phiros/RIOT,LudwigOrtmann/RIOT,OlegHahm/RIOT,LudwigKnuepfer/RIOT,ntrtrung/RIOT,syin2/RIOT,MarkXYang/RIOT,yogo1212/RIOT,jferreir/RIOT,gbarnett/RIOT,authmillenon/RIOT,jferreir/RIOT,arvindpdmn/RIOT,miri64/RIOT,BytesGalore/PetersRIOT,A-Paul/RIOT,LudwigOrtmann/RIOT,sgso/RIOT,RBartz/RIOT,MohmadAyman/RIOT,automote/RIOT,DipSwitch/RIOT,AnonMall/RIOT,neumodisch/RIOT,shady33/RIOT,phiros/RIOT,wentaoshang/RIOT,RubikonAlpha/RIOT,zhuoshuguo/RIOT,herrfz/RIOT-old,asanka-code/RIOT,malosek/RIOT,plushvoxel/RIOT,jbeyerstedt/RIOT-OTA-update,beurdouche/RIOT,Darredevil/RIOT,rfswarm/RIOT,JensErdmann/RIOT,RBartz/RIOT,zhuoshuguo/RIOT,BytesGalore/RIOT,emmanuelsearch/RIOT,Osblouf/RIOT,thomaseichinger/RIOT,locicontrols/RIOT,patkan/RIOT,kaleb-himes/RIOT,khhhh/RIOT,A-Paul/RIOT,lazytech-org/RIOT,latsku/RIOT,robixnai/RIOT,AnonMall/RIOT,jasonatran/RIOT,jfischer-phytec-iot/RIOT,zhuoshuguo/RIOT,alex1818/RIOT,thiagohd/RIOT,rfswarm/RIOT,A-Paul/RIOT,JensErdmann/RIOT,1blankz7/RIOT,automote/RIOT,cladmi/RIOT,mziegert/RIOT,yogo1212/RIOT,adjih/RIOT,benoit-canet/RIOT,alignan/RIOT,JensErdmann/RIOT,fnack/RIOT,ThanhVic/RIOT,basilfx/RIOT,automote/RIOT,mziegert/RIOT,authmillenon/RIOT,katezilla/RIOT,Josar/RIOT,yogo1212/RIOT,basilfx/RIOT,msolters/RIOT,roberthartung/RIOT,latsku/RIOT,Lotterleben/RIOT,BytesGalore/PetersRIOT,LudwigOrtmann/RIOT,jbeyerstedt/RIOT-OTA-update,kushalsingh007/RIOT,kb2ma/RIOT,abkam07/RIOT,robixnai/RIOT,herrfz/RIOT-old,josephnoir/RIOT,alex1818/RIOT,ThanhVic/RIOT,Lexandro92/RIOT-CoAP,openkosmosorg/RIOT,abkam07/RIOT,Josar/RIOT,ros2/ros2_embedded_riot,mtausig/RIOT,rakendrathapa/RIOT,l3nko/RIOT,syin2/RIOT,adjih/RIOT,gbarnett/RIOT,kbumsik/RIOT,stevenj/RIOT,alignan/RIOT,MohmadAyman/RIOT,A-Paul/RIOT,d00616/RIOT,bartfaizoltan/RIOT,rakendrathapa/RIOT,ant9000/RIOT,brettswann/RIOT,mfrey/RIOT,BytesGalore/PetersRIOT,OTAkeys/RIOT,koenning/RIOT,RIOT-OS/RIOT,sgso/RIOT,changbiao/RIOT,Darredevil/RIOT,locicontrols/RIOT,marcosalm/RIOT,altairpearl/RIOT,EmuxEvans/RIOT,MonsterCode8000/RIOT,gebart/RIOT,cladmi/RIOT,malosek/RIOT,changbiao/RIOT,sgso/RIOT,alignan/RIOT,MonsterCode8000/RIOT,arvindpdmn/RIOT,authmillenon/RIOT,alex1818/RIOT,patkan/RIOT,x3ro/RIOT,FrancescoErmini/RIOT,openkosmosorg/RIOT,Lotterleben/RIOT,x3ro/RIOT,nsol-nmsu/RIOT,asanka-code/RIOT,RubikonAlpha/RIOT,rakendrathapa/RIOT,openkosmosorg/RIOT,LudwigOrtmann/RIOT,altairpearl/RIOT,attdona/RIOT,latsku/RIOT,marcosalm/RIOT,benoit-canet/RIOT,msolters/RIOT,daniel-k/RIOT,syin2/RIOT,aeneby/RIOT,backenklee/RIOT,msolters/RIOT,msolters/RIOT,rfswarm/RIOT,dhruvvyas90/RIOT,l3nko/RIOT,avmelnikoff/RIOT,rajma996/RIOT,altairpearl/RIOT,neiljay/RIOT,luciotorre/RIOT,rakendrathapa/RIOT,dailab/RIOT,patkan/RIOT,bartfaizoltan/RIOT,josephnoir/RIOT,thiagohd/RIOT,neiljay/RIOT,MonsterCode8000/RIOT,locicontrols/RIOT,alex1818/RIOT,jasonatran/RIOT,Yonezawa-T2/RIOT,dailab/RIOT,Lotterleben/RIOT,LudwigKnuepfer/RIOT,immesys/RiSyn,herrfz/RIOT-old,aeneby/RIOT,arvindpdmn/RIOT,chris-wood/RIOT,ntrtrung/RIOT,binarylemon/RIOT,biboc/RIOT,Yonezawa-T2/RIOT,jbeyerstedt/RIOT-OTA-update,l3nko/RIOT,rfuentess/RIOT,ThanhVic/RIOT,rakendrathapa/RIOT,koenning/RIOT,TobiasFredersdorf/RIOT,PSHIVANI/Riot-Code,phiros/RIOT,adjih/RIOT,patkan/RIOT,MarkXYang/RIOT,abkam07/RIOT,chris-wood/RIOT,alignan/RIOT,Darredevil/RIOT,immesys/RiSyn,altairpearl/RIOT,biboc/RIOT,dhruvvyas90/RIOT,avmelnikoff/RIOT,mfrey/RIOT,RBartz/RIOT,sumanpanchal/RIOT,MohmadAyman/RIOT,jremmert-phytec-iot/RIOT,kerneltask/RIOT,backenklee/RIOT,rajma996/RIOT,gautric/RIOT,rfswarm2/RIOT,mfrey/RIOT,jfischer-phytec-iot/RIOT,toonst/RIOT,TobiasFredersdorf/RIOT,ros2/ros2_embedded_riot,khhhh/RIOT,Ell-i/RIOT,watr-li/RIOT,gebart/RIOT,roberthartung/RIOT,thomaseichinger/RIOT,attdona/RIOT,aeneby/RIOT,backenklee/RIOT,Darredevil/RIOT,ntrtrung/RIOT,BytesGalore/PetersRIOT,RubikonAlpha/RIOT,herrfz/RIOT,robixnai/RIOT,binarylemon/RIOT,thiagohd/RIOT,ximus/RIOT,centurysys/RIOT,openkosmosorg/RIOT,abkam07/RIOT,ks156/RIOT,sumanpanchal/RIOT,gbarnett/RIOT,ntrtrung/RIOT,AnonMall/RIOT,gebart/RIOT,kaspar030/RIOT,backenklee/RIOT,RubikonAlpha/RIOT,gautric/RIOT,RIOT-OS/RIOT,aeneby/RIOT,watr-li/RIOT,robixnai/RIOT,ntrtrung/RIOT,Hyungsin/RIOT-OS,khhhh/RIOT,jferreir/RIOT,attdona/RIOT,d00616/RIOT,l3nko/RIOT,jfischer-phytec-iot/RIOT,PSHIVANI/Riot-Code,kushalsingh007/RIOT,neumodisch/RIOT,OlegHahm/RIOT,MarkXYang/RIOT,Lotterleben/RIOT,DipSwitch/RIOT,FrancescoErmini/RIOT,brettswann/RIOT,khhhh/RIOT,phiros/RIOT,dailab/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,yogo1212/RIOT,TobiasFredersdorf/RIOT,fnack/RIOT,l3nko/RIOT,kYc0o/RIOT,miri64/RIOT,beurdouche/RIOT,kerneltask/RIOT,aeneby/RIOT,RubikonAlpha/RIOT,nsol-nmsu/RIOT,ros2/ros2_embedded_riot,jhollister/RIOT,centurysys/RIOT,ros2/ros2_embedded_riot,bartfaizoltan/RIOT,rousselk/RIOT,smlng/RIOT,herrfz/RIOT,MonsterCode8000/RIOT,patkan/RIOT,authmillenon/RIOT,changbiao/RIOT,immesys/RiSyn,Osblouf/RIOT,rfuentess/RIOT,BytesGalore/PetersRIOT,adrianghc/RIOT,RubikonAlpha/RIOT,Josar/RIOT,miri64/RIOT,Lexandro92/RIOT-CoAP,cladmi/RIOT,haoyangyu/RIOT,brettswann/RIOT,latsku/RIOT,lebrush/RIOT,Josar/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,BytesGalore/RIOT,robixnai/RIOT,rajma996/RIOT,watr-li/RIOT,jbeyerstedt/RIOT-OTA-update,avmelnikoff/RIOT,lebrush/RIOT,Darredevil/RIOT,LudwigKnuepfer/RIOT,Osblouf/RIOT,rousselk/RIOT,bartfaizoltan/RIOT,Lexandro92/RIOT-CoAP,OlegHahm/RIOT,centurysys/RIOT,jasonatran/RIOT,rfswarm2/RIOT,gautric/RIOT,tdautc19841202/RIOT,MarkXYang/RIOT,gautric/RIOT,alex1818/RIOT,LudwigOrtmann/RIOT,automote/RIOT,Osblouf/RIOT,Lotterleben/RIOT,rfuentess/RIOT,toonst/RIOT,A-Paul/RIOT,locicontrols/RIOT,miri64/RIOT,ThanhVic/RIOT,immesys/RiSyn,jhollister/RIOT,LudwigKnuepfer/RIOT,jbeyerstedt/RIOT-OTA-update,benoit-canet/RIOT,Ell-i/RIOT,TobiasFredersdorf/RIOT,thiagohd/RIOT,d00616/RIOT,arvindpdmn/RIOT,gbarnett/RIOT,dkm/RIOT,dhruvvyas90/RIOT,immesys/RiSyn,jhollister/RIOT,changbiao/RIOT,mfrey/RIOT,tfar/RIOT,gebart/RIOT,kb2ma/RIOT,FrancescoErmini/RIOT,brettswann/RIOT,hamilton-mote/RIOT-OS,binarylemon/RIOT,BytesGalore/RIOT,wentaoshang/RIOT,binarylemon/RIOT,kushalsingh007/RIOT,ros2/ros2_embedded_riot,msolters/RIOT,mziegert/RIOT,x3ro/RIOT,dhruvvyas90/RIOT,kYc0o/RIOT,katezilla/RIOT,dkm/RIOT,hamilton-mote/RIOT-OS,biboc/RIOT,tdautc19841202/RIOT,ks156/RIOT,watr-li/RIOT,avmelnikoff/RIOT,malosek/RIOT,kushalsingh007/RIOT,kb2ma/RIOT,ximus/RIOT,mtausig/RIOT,plushvoxel/RIOT,malosek/RIOT,dhruvvyas90/RIOT,BytesGalore/RIOT,kaleb-himes/RIOT,jremmert-phytec-iot/RIOT,mziegert/RIOT,syin2/RIOT,attdona/RIOT,openkosmosorg/RIOT,smlng/RIOT,kerneltask/RIOT,katezilla/RIOT,dailab/RIOT,herrfz/RIOT,jremmert-phytec-iot/RIOT,Hyungsin/RIOT-OS,OlegHahm/RIOT,basilfx/RIOT,ximus/RIOT,wentaoshang/RIOT,backenklee/RIOT,sumanpanchal/RIOT,kb2ma/RIOT,wentaoshang/RIOT,JensErdmann/RIOT,rajma996/RIOT,koenning/RIOT,wentaoshang/RIOT,basilfx/RIOT,herrfz/RIOT,ThanhVic/RIOT,MarkXYang/RIOT,rousselk/RIOT,emmanuelsearch/RIOT,TobiasFredersdorf/RIOT,brettswann/RIOT,marcosalm/RIOT,OTAkeys/RIOT,rfswarm2/RIOT,latsku/RIOT,mfrey/RIOT,abp719/RIOT,OTAkeys/RIOT,RBartz/RIOT,binarylemon/RIOT,chris-wood/RIOT,adjih/RIOT,kbumsik/RIOT,herrfz/RIOT,haoyangyu/RIOT,RBartz/RIOT,changbiao/RIOT,centurysys/RIOT,toonst/RIOT,jferreir/RIOT,cladmi/RIOT,marcosalm/RIOT,mziegert/RIOT,abp719/RIOT,luciotorre/RIOT,altairpearl/RIOT,lebrush/RIOT,stevenj/RIOT,OTAkeys/RIOT,Lotterleben/RIOT,jremmert-phytec-iot/RIOT,thomaseichinger/RIOT,thomaseichinger/RIOT,RIOT-OS/RIOT,koenning/RIOT,attdona/RIOT,sumanpanchal/RIOT,zhuoshuguo/RIOT,jhollister/RIOT,MonsterCode8000/RIOT,adrianghc/RIOT,neiljay/RIOT,jremmert-phytec-iot/RIOT,kbumsik/RIOT,neiljay/RIOT,thiagohd/RIOT,alex1818/RIOT,locicontrols/RIOT,emmanuelsearch/RIOT,koenning/RIOT,locicontrols/RIOT,rfuentess/RIOT,FrancescoErmini/RIOT,hamilton-mote/RIOT-OS,dkm/RIOT,benoit-canet/RIOT,MohmadAyman/RIOT,BytesGalore/PetersRIOT,yogo1212/RIOT,x3ro/RIOT,DipSwitch/RIOT,tdautc19841202/RIOT,tdautc19841202/RIOT,nsol-nmsu/RIOT,shady33/RIOT,1blankz7/RIOT,josephnoir/RIOT,ximus/RIOT,khhhh/RIOT,EmuxEvans/RIOT,kbumsik/RIOT,plushvoxel/RIOT,gbarnett/RIOT,rajma996/RIOT,khhhh/RIOT,centurysys/RIOT,EmuxEvans/RIOT,adrianghc/RIOT,katezilla/RIOT,1blankz7/RIOT,1blankz7/RIOT,OlegHahm/RIOT,emmanuelsearch/RIOT,PSHIVANI/Riot-Code,jasonatran/RIOT,Yonezawa-T2/RIOT,alignan/RIOT,Hyungsin/RIOT-OS,kaspar030/RIOT,DipSwitch/RIOT,PSHIVANI/Riot-Code,kerneltask/RIOT,Ell-i/RIOT,ntrtrung/RIOT,neumodisch/RIOT,dkm/RIOT,rousselk/RIOT,MohmadAyman/RIOT,dkm/RIOT,haoyangyu/RIOT,locicontrols/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,malosek/RIOT,daniel-k/RIOT,emmanuelsearch/RIOT,d00616/RIOT,nsol-nmsu/RIOT,adrianghc/RIOT,tdautc19841202/RIOT,d00616/RIOT,emmanuelsearch/RIOT,Hyungsin/RIOT-OS,tfar/RIOT,hamilton-mote/RIOT-OS,rajma996/RIOT,cladmi/RIOT,smlng/RIOT,neumodisch/RIOT,phiros/RIOT,smlng/RIOT,thomaseichinger/RIOT,asanka-code/RIOT,RIOT-OS/RIOT,abp719/RIOT,centurysys/RIOT,kbumsik/RIOT,ThanhVic/RIOT,jremmert-phytec-iot/RIOT,x3ro/RIOT,Ell-i/RIOT,kushalsingh007/RIOT,DipSwitch/RIOT,LudwigKnuepfer/RIOT,MarkXYang/RIOT,brettswann/RIOT,miri64/RIOT,latsku/RIOT,lazytech-org/RIOT,fnack/RIOT,OTAkeys/RIOT,neumodisch/RIOT,BytesGalore/PetersRIOT,stevenj/RIOT,daniel-k/RIOT,FrancescoErmini/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,rfswarm/RIOT,rfswarm/RIOT,Josar/RIOT,ros2/ros2_embedded_riot,kaspar030/RIOT,tfar/RIOT,koenning/RIOT,gebart/RIOT,ximus/RIOT,basilfx/RIOT