msm: mdss: allocate framebuffer memory from ion pool

When panel size is increased dma_alloc_coherent is not able to find
a chunk of contiguous memory big enough to hold framebuffer, this causes
framebuffer initialization to fail. Allocate buffer from ion pool which
has reserved contiguous memory at earlier stage.

Change-Id: Ibf7e3f7fc2c7ad991d69c106bbb6a9dd4c7f0e79
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>