drm/amd: add DCE 11.2 register headers

Add register headers for DCE (Display and Composition Engine)
11.2.

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