drm/msm/dp: fix panel de-initialization

During source initiated power down sequence which can
be triggered by system suspend or framework reboot,
do not clear the panel parameters as the DisplayPort
cable is still connected and rest of the sub-system
remains in connected mode. On resume, the system expect
the DisplayPort driver to be in same state as before
suspend. De-initializing the panel clears the internal
states which should be done only on hot plug event.

CRs-Fixed: 2327083
Change-Id: I78ca970155191e50166a81e29e94b7bbd82140d3
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>