drm/msm/sde: override kms post open function

Override the kms post open function to add a function call
that triggers an event notification if any of the connector's
state has changed before the client is ready. This allows
the client to appropriately handle the state change once it is
ready.

CRs-Fixed: 2079185
Change-Id: Idc84be9d335d70605ecabb2233de14654623dea3
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>