Merge pull request #9866 from kYc0o/cpu/atmega/reuse_common

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

boards/jiminy-mega256rfr2/include/board.h

boards/mega-xplained/include/board.h

boards/waspmote-pro/include/board.h

cpu/atmega1281/Makefile

cpu/atmega1281/Makefile.include

cpu/atmega1281/cpu.c

cpu/atmega1281/include/cpu_conf.h

cpu/atmega1281/startup.c

cpu/atmega1284p/Makefile

cpu/atmega1284p/Makefile.include

cpu/atmega1284p/cpu.c

cpu/atmega1284p/startup.c

cpu/atmega2560/Makefile

cpu/atmega2560/Makefile.include

cpu/atmega2560/cpu.c

cpu/atmega2560/include/cpu_conf.h

cpu/atmega2560/startup.c

cpu/atmega256rfr2/Makefile

cpu/atmega256rfr2/Makefile.include