drm/amd/display: Use sync version of indirect register access.

[Why]
Access to indirect registers by DC and other components are not synchronized.

[How]
Use sync version of indirect register access.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: JinZe.Xu <JinZe.Xu@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>