drm/amd/display: Add helper for blanking all dp displays

drm/amd/display: Add helper for blanking all dp displays

[Why & How]
1. The code to blank all dp display have been called many times,
so add helpers in dc_link to make it more concise.
2. Add some check to fix the dmesg errors at boot and resume from S3
on dcn3.1 during DQE's promotion test.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Reviewed-by: Wesley Chalmers <Wesley.Chalmers@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Leo (Hanghong) Ma <hanghong.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>