drm/amdgpu: refine vce3.0 code and related powerplay pg code.

1. not start vce3.0 when hw_init
2. stop vce3.0 when vce idle.
3. pg mask used to ctrl power down/up vce.
4. change cg pg sequence in powerplay.

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>