iommu/arm-smmu: add TZ workaround for ATOS errata

Thulium v1 has an ATOS hardware errata that requires that we call into
TZ to do some fixups.  Add a DT option to enable this workaround.

Change-Id: Ida2fecf1b40ba0f37c9cacc4296b0e8e46db071c
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>