iommu/arm-smmu: Return IOVA in iova_to_phys when SMMU is bypassed

For software initiated address translation, when domain type is
IOMMU_DOMAIN_IDENTITY i.e SMMU is bypassed, mimic HW behavior
i.e return the same IOVA as translated address.

This patch is an extension to Will Deacon's patchset
"Implement SMMU passthrough using the default domain".

Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>