Many simple kconfig configurations are added to boards and brought in with the board name.
This makes a common import of these configs so one only requires adding a BOARD.config without having to alter the makefile.
cpu/$(CPU)/Makefile.features and cpu/$(CPU)/Makefile.dep are
automatically included
Part of moving CPU/CPU_MODEL definition to Makefile.features to have it
available before Makefile.include.
