common: dma-mapping: make dma_common_contiguous_remap more robust

Large allocations can result in the dma_common_contiguous_remap
call not being able to succeed because it can't find enough
contiguous memory to setup the mapping.
Make dma_common_contiguous_remap more robust by using vmalloc
as a fallback.

Change-Id: I12ca710b4c24f4ef24bc33a0d1d4922196fb7492
Signed-off-by: Liam Mark <lmark@codeaurora.org>