Add missing gca MMIO registers and defines necessary for the next patch which re-works a lot of gfx v6 to use the new SI headers. Signed-off-by: Tom St Denis <tom.stdenis@amd.com> Reviewed-by: Alex Deucher <alexander.deucher@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>