drm/amd/powerplay: init vega20 uvd/vce powergate status on dpm setup

This is essentially necessary when uvd/vce dpm is not enabled yet.

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