Document the GEM domains exposed to userspace.
Suggested-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NSamuel Li <Samuel.Li@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>