this adds support for energy micro's efm32 tiny gecko, gecko, leopard gecko and
giant gecko series.
also, the experimental libopencmsis is included in this branch, as it is
required for full operation of the free energymicro standard library
as header file generation is not directly controlled by make (which, by
the way, makes the generatedheaders target phony), the script has to
take care of not needlessly generating files itself lest to have make
rebuild everything everytime
now tries to mkdir its way to the output files
this wouldn't be a problem currently if it wasn't for the efm32 data
lingering in the wrong branch, but otoh it's just on the safe side in
case we meet architectures that don't need other specializations at all.
