drm/amd/display: Support synchronized indirect reg access

[Why]
indirect register index/data pair may be used by multi-threads.  when it
happens, it would cause register access issue that is hard to trace.

[How]
Using cgs service, which provide a sync indirect reg access api.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Roy Chan <roy.chan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>