disp: msm: send power_on event in dual display composer kill scenario

On composer kill event, drm lastclose occurs during which suspend
commit gets triggered on primary. If secondary display is stuck in
continuous splash, then we do a early return without triggering this
suspend commit. On composer start, userspace waits for power on
event, but the drm_driver has never entered suspend state, so power
on event is never sent to userspace. This causes HWC deadlock side
effect and the current change triggers null_commit on secondary
display and then issues a suspend commit on both the displays to
avoid this deadlock issue.

Change-Id: I126f43ba3dd2c3bfa83346e8fd4678f35527893d
Signed-off-by: Jayaprakash Madisetty <quic_jmadiset@quicinc.com>