drm/amd/display: Add DPCD writes at key points

This reverts commit "Revert "Add DPCD writes at key points" ".
The following patch will fix the system hang issue.

v2: squash in indentation warning fix

Signed-off-by: Leo (Hanghong) Ma <hanghong.ma@amd.com>
Acked-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>