drm/amdgpu: refine uvd pg code in kv_dpm.c

1. no need to set cg as use hw dynamic cg.
2. when uvd idle, stop uvd. encode, start uvd.
3. if pg feature enabled, power on/down uvd by smu.
4. drm/amdgpu: dpm do not set uvd pg status.

Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>