iommu: Add domain attribute to make faults non-fatal

During development, any IOMMU faults most likely need to be debugged
immediately.  Allowing the system to continue to run has a tendency to
mask the original problem, which makes debugging more difficult.  Some
drivers might want to make all faults fatal by default, unless
explicitly requested otherwise by a client.  Add a domain attribute for
this.

Change-Id: I454b143ea3cae1f3de36e0888afd15936aa63ce1
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>