msm: mdss: fix deadlock between commit thread and shutdown

There is a deadlock in use cases where fb shutdown
is called. To avoid this condition we need to
kill display thread before release happens during
shutdown.

Change-Id: I24b03e60179c605a8572b5a011d746002e26ca18
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>