msm: pil: Use dma_alloc_coherent instead of Ion

The Ion memory manager was never intended for a use case such
as PIL. Instead, use dma_alloc_coherent to allocate the necessary
memory. Individual regions of memory will be setup elsewhere to
be tied to the individual PIL regions for allocation.

Change-Id: Ibad05113a0337cad8270a1a6a4fdcfcf60c0a9a0
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>