drm/amd/display: Set watermarks set D equal to A

[Description]
- Since we do not use optimized watermark settings for MALL,
  set D = A
- PMFW uses Set D for d0i3.1, so driver should make D = A for the
  time being
- If we choose to optimize in the future we can set watermarks D
  correctly

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>