dma-mapping-fast: Add support for DMA_ATTR_FORCE_CONTIGUOUS

Allow devices with an iommu to allocate from a cma area if
the DMA_ATTR_FORCE_CONTIGUOUS flag is given.

Change-Id: Ifd8575d1cea57cbc13c602f6edb6ab389844b35d
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>
[isaacm@codeaurora.org: resolved merge conflicts]
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>