smu_send_smc_msg(smu, SMU_MSG_AllowGfxOff) Just turn on a switch.

As to when GPU get into "GFXoff" will be up to drawing load.

So we can not sure which state GPU should be in after enable gfxoff
feature.
Signed-off-by: Nchen gong <curry.gong@amd.com>
Acked-by: NEvan Quan <evan.quan@amd.com>
Reviewed-by: NKevin Wang <kevin1.wang@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>