disp: msm: sde: wait for cwb done before transitioning to secure

There are some scenarios where the secure commit
can come when the previous cwb commit is going on.
Add support to wait for cwb commit to be completed
before making the transition to secure.

Change-Id: I95d10ecb5b682e60c059588db926f765a0c7c381
Signed-off-by: Krishna Manikandan <mkrishn@codeaurora.org>