drm/amd/display: Add connector HPD trigger debugfs entry

[why]
Need a tool to retrigger a virtual hotplug for testing purposes with
force redetection in both DC and DM.

[how]
Emulate handle_hpd_irq for connector as if usermode would trigger
a hotplug. Perform DC link discovery, DM connector update, and
DM force atomic commit.

In order to trigger HPD on the connector user needs to echo 1 into
"trigger_hotplug" debugfs entry on its respective connector.

Signed-off-by: Eryk Brol <eryk.brol@amd.com>
Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Mikita Lipski <Mikita.Lipski@amd.com>
Acked-by: Eryk Brol <eryk.brol@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>