arm64: dma_mapping: Implement .dma_supported()

The dma_supported() API checks to see if the device can support DMA to
the memory described by the mask.  Implement this for the DMA IOMMU
mapper by calling into the IOMMU's iommu_dma_supported API.

Change-Id: I5e31e386cd40c3f3312e1be1ca516c6e72213547
Signed-off-by: Neeti Desai <neetid@codeaurora.org>
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>