drm/amd/powerplay: initialize uvd/vce powergate status v4

On UVD/VCE dpm enabled/disabled, the powergate status will be
set as false/true. So that we will not try to ungate/gate them(
enable/disable their dpm) again.

v2: added check for uvd/vce powergate status before gating
v3: fix typo in description
v4: warning fix (Alex)

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>