iommu/arm-smmu: workaround some ATOS hw errata

qcom,smmuv2 has a hardware errata that requires that the SMMU be halted
during atos operations

Change-Id: Ic40c7b93d64eebb97fe77082d8335debab624af1
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>