tests/periph_flashpage: test unaligned write for sam0
tests/periph_flashpage: test unaligned write for sam0

Adds test of unaligned write to already integrated sam0_common config area test.

kaspar030/RIOT,kYc0o/RIOT,OlegHahm/RIOT,kaspar030/RIOT,kYc0o/RIOT,jasonatran/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,miri64/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,jasonatran/RIOT,jasonatran/RIOT,authmillenon/RIOT,OTAkeys/RIOT,kaspar030/RIOT,ant9000/RIOT,authmillenon/RIOT,jasonatran/RIOT,OTAkeys/RIOT,kaspar030/RIOT,ant9000/RIOT,ant9000/RIOT,ant9000/RIOT,miri64/RIOT,miri64/RIOT,kYc0o/RIOT,authmillenon/RIOT,OTAkeys/RIOT,authmillenon/RIOT,OlegHahm/RIOT,authmillenon/RIOT,miri64/RIOT,ant9000/RIOT,authmillenon/RIOT,miri64/RIOT,kYc0o/RIOT,kYc0o/RIOT