iommu: Add support for .dma_supported() ops

The .dma_supported() checks to see if the device can support DMA to the
memory described by the mask.  Add support for this operation in the
iommu layer

Change-Id: Icf37b9540aa68c2be3fd603a48402d6fcccd8208
Signed-off-by: Neeti Desai <neetid@codeaurora.org>
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>