drm/amdgpu/dpm: add new callback to fetch vce clock state (v2)

Will be used by the new info ioctl query.

v2: fetch a single state per request

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