ppc/pnv: Make HOMER memory a RAM region

ppc/pnv: Make HOMER memory a RAM region

The HOMER is a region of memory used by host and firmware and
microconrollers. It has very little logic by itself, just some BAR
registers. Users of this memory should operate on it rather than
have HOMER implement them with MMIO registers, which is not the
right model.

This change switches the implementation of HOMER from MMIO to RAM,
and moves the OCC register implementation to in-memory structure
accesses performed by the OCC model.

This has the downside that access to unimplemented regions of HOMER
are no longer flagged. Perhaps that could be done by adding a memory
region for HOMER, and ram subregions under that for each implemented
part. But for now this takes the simpler approach.

Note: This brings some data structure definitions from skiboot, which
does not match QEMU coding style but is not changed to make comparisons
and updates simpler.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>