msm: mdss: Allocate fb memory under 4GB physical address space

Linux kernel framework of framebuffer APIs do not support LPAE systems.
These APIs are using "unsigned long" data type instead of "phys_addr_t"
for physical addresses which doesn't work with LPAE systems. Until
framebuffer APIs are fixed, allocate fb memory on MSM chip-sets using
dma_alloc_coherent and GFP_KERNEL to get the memory from below 4GB
physical address space.

Conflicts:
	Documentation/devicetree/bindings/fb/mdss-mdp.txt

Change-Id: Ieca41cae21c956a8b4cf1d5729d287bb0bb30f8d
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>