drm/amd/powerplay: always use fast UCLK switching when UCLK DPM enabled

With UCLK DPM enabled, slow switching is not supported any more.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>