drm/amd/display: Refactor and add visual confirm for HW Flip Queue

[Why]
Visual confirm will indicate if driver is programming
the surface address.
Refactor is required because much of the visual confirm
logic is buried deep in the mpcc files.
In addition, visual confirm is not updated during fast updates.

[How]
In order to have visual confirm for driver flips, visual confirm
needs to be updated on every frame, including fast updates.
Add a new hw sequencer interface update_visual_confirm_color,
and a new mpc function pointer set_bg_color.

v2: drop unused variable (Alex)

Signed-off-by: Wyatt Wood <wyatt.wood@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>