iommu/arm-smmu: Do an ATOS in the fault handler

In order to facilitate debugging of context faults, the result of a
software table walk is currently printed as part of the fault handling.
However, there are certain bugs and error conditions that can't be
caught by doing a software table walk (like missing TLB invalidation or
misbehaving hardware).  Add a hardware table walk (via ATOS) to improve
debugging capabilities.

Change-Id: Ie89019df62f115627359e29b1f6cc5de3a36d1b5
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>