msm_fb : Add option to enable/disable  mixer commit

Adds support to enable or disable mixer commit during pipe
staging operations. Depending on the current activity, this
selection can be made.

Change-Id: Ia2f5dbab58f73ef4de90abf7f278332d8d73df46
Signed-off-by: Pradeep Jilagam <pjilagam@codeaurora.org>

Conflicts:

	drivers/video/msm/mdp4_overlay.c
	drivers/video/msm/mdp4_overlay_mddi.c