fbdev: msm: Fix race condition during te_irq calls

Add lock to synchronize te_irq calls from both the dsi
blank/unblank and wait4pingpong function calls.

Change-Id: If59e7efe55ff8f7f9eb61d6297aefedb857e7abf
Signed-off-by: Raghavendra Ambadas <rambad@codeaurora.org>