Required for gfx powergating.

Change-Id: I5a2f8f41253686d8bb776a92aa68bf90877ebaa8
Signed-off-by: NHawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: NChunming Zhou <david1.zhou@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>