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.

CRs-Fixed: 959535
Change-Id: I3106a98370a70611f4670aaf1c0f95c9e758a87c
Signed-off-by: Susheel Khiani <skhiani@codeaurora.org>