drm/amd/powerplay: implement sysfs of pp_force_state for sw-smu

the SMU v11 doesn’t support pp_force_state so far, so we didn’t implement
it.

Signed-off-by: Kevin Wang <Kevin1.Wang@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>