disp: msm: fix vsync wait for poms and dms

SDE RSC does not need to wait for vsync during
dms. It was removed unintentionally with commit
a74d2cf7fa2f ("disp: msm: add runtime_pm ops
support in drm driver"). However, Panel mode
switch still needs vsync wait based on
recommendation. This change fixes vsync wait
for both cases.

Change-Id: Ic9119132eb15a8c33f3841ba5df2624189d93395
Signed-off-by: Lei Chen <chenlei@codeaurora.org>