[Why]
Panel control always programs instance 0. With multi eDP we need to
support multiple instances.

[How]
Use link index to set different instances for panel control.
Refactored LVTMA control to support multiple instances.
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Jake Wang <haonan.wang2@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Eryk Brol <eryk.brol@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>