drm/amd/display: add config option for eDP hotplug detection

[Why]
Some custom platforms use eDP hotplug events to notify panel
capability changes that should be reported

[How]
Add a DC config option that unblocks eDP hotplug events

Signed-off-by: Yi-Ling Chen <Yi-Ling.Chen2@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>