disp: msm: update vblank queue mechanism

If vblank call is queued to both commit & event thread,
in few cases, the order in which vblank call is queued and
order in which the execution takes place might differ
resulting in bad state machine. This change adds mutex lock
mechanism to avoid enabling irq duing modeset and also
reverts earlier commit 7ba450fa ("disp: msm: queue
vblank work on disp thread during modeset").

Change-Id: Ifdf0502aee3f4cf911b1596aae2a9f2f648d9919
Signed-off-by: Yashwanth <yvulapu@codeaurora.org>