drm/msm/dp: fix suspend/resume hot plug handling

If the device is going into suspend and then resumed,
handle the power on sequence gracefully. Cable may have
been removed during suspend. On resume, let the DisplayPort
driver come up with the same settings it went to sleep.
In case the cable remains connected, it will join back the
previous session. If the cable is removed, DisplayPort
driver eventually receives the cable disconnect notification
on resume and handles it same way as normal hot plug.

CRs-Fixed: 2296893
Change-Id: Ie6c1da154cc0a2e03cf85b7383479b1dd3028873
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>
Signed-off-by: Divya Sharma <divyash@codeaurora.org>