drm/amd/amdgpu: enable mmhub and athub cg on gc 12.0.0

Enable mmhub and athub cg on gc 12.0.0

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>