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