drm/msm/dp: handle DisplayPort ON/OFF during PM suspend/resume

Add changes in the DisplayPort ON/OFF path and the HPD notification
path to handle PM suspend/resume and adb shell stop/start use-cases
which are not driven by HPD events.

Change-Id: Iedccae9104eb8937d1fd5f4ce958ad5818a2c3ff
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>