msm: display: add mutex for display driver entries

In some cases, display driver is called by multiple threads, this
will cause re-entrance problem. For example, one thread is
calling display commit, the other turns off the display. In order
to serialize the operation, mutex is added to most APIs.
Only the ones for initialization won't be added.

(cherry picked from commit 12c51684416bf5cc14d645fb741eea8d3d6627fa)

Change-Id: I84359d2e89930b61f5a0641b5e3078f9846c60ab
Signed-off-by: Ken Zhang <kenz@codeaurora.org>
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>

Conflicts:

	drivers/video/msm/msm_fb.c

Conflicts:
	drivers/video/msm/msm_fb.c