sys,fmt: simplify fmt_s16_dfp
sys,fmt: simplify fmt_s16_dfp

    - allow formating of val=12345 with fp_digits=6 as 0.012345
    - use assert instead of explicit if
    - remove unused pwr function

RIOT-OS/RIOT,cladmi/RIOT,LudwigKnuepfer/RIOT,basilfx/RIOT,hamilton-mote/RIOT-OS,kYc0o/RIOT,biboc/RIOT,adjih/RIOT,cladmi/RIOT,aeneby/RIOT,A-Paul/RIOT,x3ro/RIOT,lazytech-org/RIOT,A-Paul/RIOT,miri64/RIOT,toonst/RIOT,roberthartung/RIOT,ant9000/RIOT,neiljay/RIOT,adrianghc/RIOT,yogo1212/RIOT,A-Paul/RIOT,OlegHahm/RIOT,immesys/RiSyn,mfrey/RIOT,mtausig/RIOT,miri64/RIOT,hamilton-mote/RIOT-OS,mfrey/RIOT,x3ro/RIOT,Josar/RIOT,x3ro/RIOT,LudwigKnuepfer/RIOT,kYc0o/RIOT,BytesGalore/RIOT,toonst/RIOT,josephnoir/RIOT,immesys/RiSyn,roberthartung/RIOT,biboc/RIOT,lazytech-org/RIOT,lazytech-org/RIOT,immesys/RiSyn,avmelnikoff/RIOT,mtausig/RIOT,immesys/RiSyn,LudwigKnuepfer/RIOT,kbumsik/RIOT,mfrey/RIOT,adjih/RIOT,gebart/RIOT,ant9000/RIOT,lazytech-org/RIOT,rfuentess/RIOT,OTAkeys/RIOT,neiljay/RIOT,beurdouche/RIOT,yogo1212/RIOT,basilfx/RIOT,gebart/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,roberthartung/RIOT,cladmi/RIOT,josephnoir/RIOT,yogo1212/RIOT,hamilton-mote/RIOT-OS,ant9000/RIOT,toonst/RIOT,toonst/RIOT,adjih/RIOT,roberthartung/RIOT,adjih/RIOT,josephnoir/RIOT,avmelnikoff/RIOT,ks156/RIOT,beurdouche/RIOT,kbumsik/RIOT,smlng/RIOT,yogo1212/RIOT,kYc0o/RIOT,miri64/RIOT,avmelnikoff/RIOT,authmillenon/RIOT,neiljay/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,adrianghc/RIOT,lazytech-org/RIOT,rfuentess/RIOT,biboc/RIOT,adjih/RIOT,adrianghc/RIOT,jasonatran/RIOT,LudwigOrtmann/RIOT,kbumsik/RIOT,rfuentess/RIOT,authmillenon/RIOT,kaspar030/RIOT,smlng/RIOT,roberthartung/RIOT,neiljay/RIOT,kYc0o/RIOT,josephnoir/RIOT,immesys/RiSyn,jasonatran/RIOT,rfuentess/RIOT,mfrey/RIOT,Josar/RIOT,jasonatran/RIOT,BytesGalore/RIOT,LudwigOrtmann/RIOT,smlng/RIOT,BytesGalore/RIOT,yogo1212/RIOT,BytesGalore/RIOT,LudwigKnuepfer/RIOT,OTAkeys/RIOT,josephnoir/RIOT,immesys/RiSyn,toonst/RIOT,LudwigOrtmann/RIOT,ks156/RIOT,authmillenon/RIOT,hamilton-mote/RIOT-OS,LudwigKnuepfer/RIOT,aeneby/RIOT,kaspar030/RIOT,hamilton-mote/RIOT-OS,gebart/RIOT,smlng/RIOT,LudwigOrtmann/RIOT,A-Paul/RIOT,A-Paul/RIOT,rfuentess/RIOT,mtausig/RIOT,ks156/RIOT,cladmi/RIOT,biboc/RIOT,mtausig/RIOT,ks156/RIOT,ant9000/RIOT,x3ro/RIOT,biboc/RIOT,LudwigOrtmann/RIOT,kaspar030/RIOT,OlegHahm/RIOT,authmillenon/RIOT,BytesGalore/RIOT,x3ro/RIOT,kaspar030/RIOT,yogo1212/RIOT,neiljay/RIOT,mfrey/RIOT,LudwigOrtmann/RIOT,beurdouche/RIOT,mtausig/RIOT,OlegHahm/RIOT,ks156/RIOT,Josar/RIOT,beurdouche/RIOT,basilfx/RIOT,OTAkeys/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,smlng/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,miri64/RIOT,kYc0o/RIOT,avmelnikoff/RIOT,Josar/RIOT,cladmi/RIOT,beurdouche/RIOT,kbumsik/RIOT,gebart/RIOT,adrianghc/RIOT,aeneby/RIOT,basilfx/RIOT,Josar/RIOT,authmillenon/RIOT,aeneby/RIOT,ant9000/RIOT,kbumsik/RIOT,basilfx/RIOT,kaspar030/RIOT,adrianghc/RIOT,miri64/RIOT,aeneby/RIOT,gebart/RIOT,avmelnikoff/RIOT