msm_fb: display: Add support for 4 layer MDP composition

Add 4 layers composition support to MDP by allowing borderfill
pipe to be used as base layer of mdp blending. This releases
RGB1 base pipe which can be used as a general purpose pipe.

Change-Id:I517485d738e8bb555a263b3ea885d78d5e4f4396
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>

Conflicts:

	drivers/video/msm/mdp4.h
	drivers/video/msm/mdp4_overlay.c
	drivers/video/msm/mdp4_overlay_lcdc.c