This adds unit test for microkernel private FIFOs.
The code piggybacks to the public FIFOs tests (by
including the same source file), so any updates to
the test will be applied to both.
Note that the prj.mdef are different for both tests, since
the private FIFOs test move some of the FIFOs
inside source code.
Change-Id: I4130ac540b10a31cd30f37890e9cc389af73e89b
Signed-off-by: Daniel Leung <daniel.leung@intel.com>