disp: msm: dp: reset disconnect flags on cable hotplug

When a physical DP sink is connected after a simulation
session, the attention events from the sink are ignored.
The forced_disconnect flag prevents handling of attention
events when disconnect is simulated or forced. This flag
does not get reset when a physical sink is connected.
Certain sinks which lose link integrity after link
training sequence fail to display image.

This change will reset the flag so that the attention
events which occur after the cable hotplug can be processed.

Change-Id: Ie551ead19ecff0e93da48acc2dbb1d761c55fa20
Signed-off-by: Sankeerth Billakanti <sbillaka@codeaurora.org>