arm: 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 of our use cases we
actually want the entire sg list mapped into the SMMU as a single
contiguous range.

This was missing for arm 32bit, add it.

Change-Id: Ibf67f29a60b8d19e526c4719590f2f473ea9dca5
Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>