r600g: implement compression for MSAA colorbuffers for evergreen

r600g: implement compression for MSAA colorbuffers for evergreen

This adds the FMASK and CMASK buffers. They share the same resource
with color data.

COMPRESSION and FAST_CLEAR are always enabled if both FMASK and CMASK are
allocated. We initialize the CMASK to a "compressed" state (not "fast cleared"),
so that we can keep FAST_CLEAR enabled all the time.

Both FMASK and CMASK must be present at the moment. If either one is missing,
the other one is not used.

v2: add cayman regs in the list

Reviewed-by: Jerome Glisse <jglisse@redhat.com>