drm/amd/display: Add 3DLUT DMA load trigger

drm/amd/display: Add 3DLUT DMA load trigger

[Why/How]
Need to be able to trigger a DMA load to update 3DLUT contents in MPC.
Adding a HWSS function to serve as the trigger.

Reviewed-by: Krunoslav Kovac <krunoslav.kovac@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Ilya Bakoulin <ilya.bakoulin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>