boards/common/arduino-atmega: define led_init as weak
boards/common/arduino-atmega: define led_init as weak

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