arm64: dma-mapping: map sg lists into the SMMU as virtually contiguous

In arm_iommu_map_sg, currently we map each individual link in the given
scatterlist into the SMMU individually such that they may or may not be
virtually contiguous.  However, in most (all?) of our use cases we
actually want the entire sg list mapped into the SMMU as a single
contiguous range.  Use iommu_map_range to accomplish this.

Change-Id: Icf72ece50c3120a0091dbfab1523ff11da20f807
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>