msm: mdss: serialize overlay_vsync_ctrl with ov_lock

There is a race condition between mdss_mdp_idle_pc_restore
and mdss_mdp_display_commit. Use ov_lock to serialize
execution of these two threads to fix race condition.

Change-Id: I6454e3d0edf2f3655e442d591fb3cac48f88a712
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>