dma-mapping: add support for dma-coherent-hint-cached

When clients configure their device as dma-coherent-hint-cached this will
result in the memory framework only trying to DMA map buffers as
IO-coherent if the framework is confident that the buffers are mapped as
cached in the CPU.

Clients should configure their device as dma-coherent-hint-cached instead
of dma-coherent when they need to DMA map both buffers that have cached
CPU mappings and other buffers which have uncached CPU mappings. By using
dma-coherent-hint-cached the framework will ensure that the client's
buffers with uncached CPU mappings don't get DMA mapped as IO-coherent.

Change-Id: I990184b54d4148bf952cc672ec267b51efd81473
Signed-off-by: Liam Mark <lmark@codeaurora.org>