boards/arduino-mega2560: Add Kconfig symbols
boards/arduino-mega2560: Add Kconfig symbols

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