iommu: arm-smmu: Cleanup iova_to_phys_fault

Previously a different implementation of iova_to_phys was used if called
from within an interrupt handler. Since this alternate implementation
works perfectly fine outside interrupt handlers, use it for both.

Change-Id: I280c28e5cbd700439742310dbaa6460dd0983bd0
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>