iommu: add qcom_iommu

An iommu driver for Qualcomm "B" family devices which do not completely
implement the ARM SMMU spec.  These devices have context-bank register
layout that is similar to ARM SMMU, but no global register space (or at
least not one that is accessible).

Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>