iommu: add qcom-hyp-smmu

iommu: add qcom-hyp-smmu

Add a basic implementation of the ARM SMMU. This driver is intended for
use on Qualcomm platforms where the SMMU has been configured by a previous
bootloader, cannot be turned off, and doesn't support BYPASS streams.
It keeps all existing stream mappings and only creates new ones for stream
ids that aren't already configured.

This driver is necessary to support peripherals that perform DMA which
weren't configured by the previous stage bootloader (for example USB).
It works by allocating a context bank using identity mapping (as U-Boot
doesn't use virtual addresses).

Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>