[Why]
HPD sense changes can occur during low power states and need to be
notified from firmware to driver. Upon notification the hotplug
redetection routines should execute.

[How]
Add Support in DMUB srv and DMUB srv stat for receiving these
notifications. DM can hook them up and process the HPD redetection
once received.
Reviewed-by: Duncan Ma <duncan.ma@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>