msm: iommu: Support cache-coherent memory access

Add support for allowing IOMMU memory transactions to be
cache coherent, eliminating the need for software cache
management in certain situations. This can lead to
improvements in performance and power usage, assuming the
multimedia core's access pattern exhibits spatial locality
and that its working set fits into the cache.

Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>
Signed-off-by: Daniel Walker <dwalker@codeaurora.org>