drm/amd/display: Drop reusing drm connector for MST

drm/amd/display: Drop reusing drm connector for MST

[ Upstream commit 0e6613e46fed29316f33acf86e1d1568288638b5 ]

[why]
It is not safe to keep existing connector while entire topology
has been removed. Could lead potential impact to uapi.
Entirely unregister all the connectors on the topology,
and use a new set of connectors when the topology is plugged back
on.

[How]
Remove the drm connector entirely each time when the
corresponding MST topology is gone.
When hotunplug a connector (e.g., DP2)
1. Remove connector from userspace.
2. Drop it's reference.
When hotplug back on:
1. Detect new topology, and create new connectors.
2. Notify userspace with sysfs hotplug event.
3. Reprobe new connectors, and reassign CRTC from old (e.g., DP2)
to new (e.g., DP3) connector.

Signed-off-by: Jerry (Fangzhi) Zuo <Jerry.Zuo@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>