drm/amd/powerplay: remove uncessary extra gfxoff control call

Gfxoff is already enabled in amdgpu_device_ip_set_powergating_state.
So, no need to enable it again in pp_late_init.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>