iommu/arm-smmu: Implement DOMAIN_ATTR_NON_FATAL_FAULTS

Unhandled context faults should be fatal unless explicitly requested
otherwise by the client.  Implement the DOMAIN_ATTR_NON_FATAL_FAULTS
attribute for this purpose.

Change-Id: I414fcc6000a6c47b3cbf77b1098c8b7895cbb20d
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>