iommu/arm-smmu: Wire up io-pgtable-fast for domains that request it

An io-pgtable implementation for fast 4K mappings was recently added,
and we've now implemented all of the domain attributes necessary to use
it.  Wire it up.

CRs-Fixed: 997751
Change-Id: I9ddd2dd2cad91ac3d3ccce7c0cd0abb37cd57075
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>