Merge pull request #11027 from maribu/atmega_cleanup

boards/arduino-duemilanove/Makefile.dep

boards/arduino-duemilanove/Makefile.include

boards/arduino-mega2560/Makefile.dep

boards/arduino-uno/Makefile.dep

boards/arduino-uno/Makefile.include

boards/common/arduino-atmega/Makefile.include

boards/common/arduino-atmega/include/periph_conf.h

boards/common/atmega/Makefile.include

boards/common/atmega/include/periph_conf_atmega_common.h

boards/jiminy-mega256rfr2/Makefile.include

boards/jiminy-mega256rfr2/include/periph_conf.h

boards/mega-xplained/Makefile.include

boards/mega-xplained/include/periph_conf.h

boards/waspmote-pro/Makefile

boards/waspmote-pro/Makefile.dep

boards/waspmote-pro/Makefile.include

boards/waspmote-pro/include/periph_conf.h