we can take gfx off feature as gfx power gate. gfx off feature is also
controled by smu. so add gfx_off support in pp_set_powergating_by_smu.
Reviewed-by: NEvan Quan <evan.quan@amd.com>
Signed-off-by: NRex Zhu <Rex.Zhu@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>