boards/arduino-atmega: move shared code to common/arduino-atmega

boards/arduino-duemilanove/Makefile

boards/arduino-duemilanove/Makefile.features

boards/arduino-duemilanove/Makefile.include

boards/arduino-mega2560/Makefile

boards/arduino-mega2560/Makefile.features

boards/arduino-mega2560/Makefile.include

boards/arduino-uno/Makefile

boards/arduino-uno/Makefile.features

boards/arduino-uno/Makefile.include

boards/common/arduino-atmega/Makefile

boards/common/arduino-atmega/Makefile.dep

boards/common/arduino-atmega/Makefile.features

boards/common/arduino-atmega/Makefile.include

boards/common/arduino-atmega/board.c

boards/common/arduino-atmega/dist/debug.sh

boards/common/arduino-atmega/dist/debug_srv.sh

boards/common/arduino-atmega/dist/gdb.conf

boards/common/arduino-atmega/doc.txt

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

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