iommu/arm-smmu: Add support for slave side protection

For targets where we have no hypervisor, slave side protection mechanism
is used to provide buffer protection. Add functionality to make calls
into TZ for mapping/unmapping of buffers.

Change-Id: I845983a25b56ce1b34c90f91ac4a2cf6c4451813
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>