arm64: dma-mapping: add support for IOMMU mapper

On systems with IOMMUs, it's useful to handle IOMMU mappings in the
dma-mapping layer. This is currently supported on arm but not arm64. Add
support in arm64 by gratuitously lifting most of the IOMMU-related stuff
from dma-mapping.c in arm.

The original arm work was done by Marek Szyprowski in [4ce63fcd:
"ARM: dma-mapping: add support for IOMMU mapper"].

Change-Id: I1c3c8fe15049fe456751074398fd179ebd2ec64e
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>