disp: msm: sde: wait for lp2 and pm_suspend frame trigger

PM_SUSPEND API adds extra pm_runtime refcount and calls
the device driver for pm_suspend. At this point display
device may not be in power collapse state. This patch
makes sure that crtc_commit thread is idle and triggers
power collapse also.

Change-Id: Ia21d6a6b6fd32caeb9d16fa5cf998b91ef990e01
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>