commit 6b8eeca6 upstream.

I've only seen this once, and I failed to capture the
lockdep backtrace, but I did some investigations.

If we are calling into the MST layer from EDID probing,
we have the mode_config mutex held, if during that EDID
probing, the MST hub goes away, then we can get a deadlock
where the connector destruction function in the driver
tries to retake the mode config mutex.

This offloads connector destruction to a workqueue,
and avoid the subsequenct lock ordering issue.
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>