drm/amd/pm: implement is_dpm_running() callback for yellow carp

Implement function to check if DPM is running for yellow carp.

Acked-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Xiaomeng Hou <Xiaomeng.Hou@amd.com>
Reviewed-by: Kevin Wang <kevin1.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>