drm/amd/powerplay: implement power_dpm_force_performance_level for SMU11

add get_performance_level and force_performance_level
to implement the sys interface for SMU11.

Signed-off-by: Chengming Gui <Jack.Gui@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>