sam0_common: periph/spi: use sercom_clk_en/dis()
sam0_common: periph/spi: use sercom_clk_en/dis()

Use already existing functions to turn on / off SERCOM clocks instead
of replicating the functionality in the driver.

yogo1212/RIOT,x3ro/RIOT,mtausig/RIOT,rfuentess/RIOT,x3ro/RIOT,OTAkeys/RIOT,rfuentess/RIOT,OlegHahm/RIOT,mfrey/RIOT,smlng/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,yogo1212/RIOT,smlng/RIOT,aeneby/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,jasonatran/RIOT,jasonatran/RIOT,aeneby/RIOT,cladmi/RIOT,mtausig/RIOT,x3ro/RIOT,miri64/RIOT,ant9000/RIOT,mtausig/RIOT,kYc0o/RIOT,kaspar030/RIOT,smlng/RIOT,kaspar030/RIOT,OTAkeys/RIOT,rfuentess/RIOT,aeneby/RIOT,RIOT-OS/RIOT,basilfx/RIOT,RIOT-OS/RIOT,toonst/RIOT,yogo1212/RIOT,mfrey/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,smlng/RIOT,kYc0o/RIOT,toonst/RIOT,authmillenon/RIOT,OlegHahm/RIOT,cladmi/RIOT,x3ro/RIOT,ant9000/RIOT,aeneby/RIOT,jasonatran/RIOT,rfuentess/RIOT,basilfx/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,ant9000/RIOT,basilfx/RIOT,basilfx/RIOT,ant9000/RIOT,authmillenon/RIOT,kYc0o/RIOT,yogo1212/RIOT,miri64/RIOT,authmillenon/RIOT,mfrey/RIOT,kYc0o/RIOT,toonst/RIOT,josephnoir/RIOT,RIOT-OS/RIOT,mfrey/RIOT,basilfx/RIOT,jasonatran/RIOT,mfrey/RIOT,jasonatran/RIOT,josephnoir/RIOT,kaspar030/RIOT,miri64/RIOT,mtausig/RIOT,smlng/RIOT,josephnoir/RIOT,x3ro/RIOT,yogo1212/RIOT,toonst/RIOT,miri64/RIOT,kaspar030/RIOT,josephnoir/RIOT,yogo1212/RIOT,cladmi/RIOT,authmillenon/RIOT,aeneby/RIOT,rfuentess/RIOT,cladmi/RIOT,cladmi/RIOT,mtausig/RIOT,kaspar030/RIOT,OlegHahm/RIOT,kYc0o/RIOT,miri64/RIOT,toonst/RIOT,OlegHahm/RIOT,josephnoir/RIOT,ant9000/RIOT