This removes duplication for the jlink case (keeping only any
non-default values in the board makefiles), and opens up STK3700's
OpenOCD programmability for generic boards.
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.
When it was running 'hello-world', the board could not be flashed through
JLinkExe anymore and only through the drag and drop support.
By resetting the board before doing 'loadbin' it can now be flashed
properly.
