msm_fb: display: Add SMP-safety for PPP Operations

Adds protection using spinlock for the variable used in
controlling the PPP operations

Change-Id: Iba6ef5e32d38668bd110ed23ee9631aa40de79e0
Signed-off-by: Pradeep Jilagam <pjilagam@codeaurora.org>

Conflicts:
	drivers/video/msm/mdp.c