Revert "iommu/arm-smmu: Treat all device transactions as unprivileged"

This reverts commit d346180e ("iommu/arm-smmu: Treat all device
transactions as unprivileged").

The graphics implementation uses both privileged and unpriveleged mappings
in the same context bank.

Change-Id: Ia9771d1678398393ecc30ba81debd03186a09f2d
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>