boards/saml21-xpro: configure UART & SPI on EXT2, 3
boards/saml21-xpro: configure UART & SPI on EXT2, 3

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