The mn10200-specific logic (setting up part_specific_obj) isn't used
by the build anywhere -- looks like copy & paste left overs from mips.
So punt that & merge the target_makefile_frag_path up to the top-level.
Depending on the processing order of rules when installing in parallel,
these install rules might be processed before some other rule happens
to create the respective dirs. Make sure each one creates the needed
dirs before installing into them.
