iommu/qcom: Add qcom_iommu

An iommu driver for Qualcomm "B" family devices which do implement the
ARM SMMU spec, but not in a way that is compatible with how the arm-smmu
driver is designed.  It seems SMMU_SCR1.GASRAE=1 so the global register
space is not accessible.  This means it needs to get configuration from
devicetree instead of setting it up dynamically.

In the end, other than register definitions, there is not much code to
share with arm-smmu (other than what has already been refactored out
into the pgtable helpers).

Signed-off-by: Rob Clark <robdclark@gmail.com>
Tested-by: Riku Voipio <riku.voipio@linaro.org>
Signed-off-by: Joerg Roedel <jroedel@suse.de>