Revert "arm64: dma-mapping: avoid calling iommu_iova_to_phys"

This reverts commit 0d02975d9ffd55f1c0fe5db08f45a9ee1d22f354 since it's
causing problems for some reason.  This should really be debugged but
for now just revert it.

Change-Id: I31f382c1945cd1cd84dbbd3dfb715009b8442fe9
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>