iommu: Add flags parameter to .trigger_fault

IOMMU drivers might want more control over the types of faults being
triggered with iommu_trigger_fault.  Add a flags parameter that can be
used to provide more control over the types of faults that can be
triggered.

Change-Id: I2f21b383437430e957ab52070d3575e8cb3dee90
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>