drm/amd/display: support main link off before specific vertical line

[Why]
Some panels request main link off before specific vertical line.
If source turn off main link after specific vertical line then
panel defect will be exposed.

[How]
Add interface to support turn off main link before specific
vertical line

Reviewed-by: Robin Chen <robin.chen@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Signed-off-by: Paul Hsieh <paul.hsieh@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>