iommu/arm-smmu: do TLBSYNC after TLBIALL in ATOS

We need to make sure the TLBIALL is actually done before proceeding with
the ATOS since the ATOS won't succeed if the TLB hasn't been
invalidated.  Add a TLBSYNC to ensure that it finishes.

Change-Id: I55836039d7ded5ba8889bc81ee474624e98ef491
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>