Removed any dependency from ppsi's internal copy of spec drivers, and the
drivers' source itself.

With this patch, now we ppsi is fully compatible with wrpc-sw drivers.

In order to compile ppsi main (which, in the future, will become obsolete)
you can now either:
- copy ppsi project inside the wrpc-sw dir (or, better, use the ppsi as
wrpc-sw submodule)
- go into arch-spec/Makefile and modify the WRPCSW_ROOT var
Signed-off-by: Aurelio Colosimo <aurelio@aureliocolosimo.it>