drm/amd/display: refactor programming of DRR

[Why]
Keep enable_stream_timing programming only
timing related stuff.

[How]
Move DRR and static screen mask programming from
enable_stream_timing to outside in
apply_single_controller_ctx_to_hw

Signed-off-by: Anthony Koo <Anthony.Koo@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>