drivers/passthrough: arm: Add support for SMMU drivers

This patch add support for ARM architected SMMU driver. It's based on the
linux drivers (drivers/iommu/arm-smmu) commit 89ac23cd.

The major differences with the Linux driver are:
    - Fault by default if the SMMU is enabled to translate an
    address (Linux is bypassing the SMMU)
    - Using P2M page table instead of creating new one
    - Dropped stage-1 support
    - Dropped chained SMMUs support for now
    - Reworking device assignment and the different structures

Xen is programming each IOMMU by:
    - Using stage-2 mode translation
    - Sharing the page table with the processor
    - Injecting a fault if the device has made a wrong translation

Signed-off-by: Julien Grall<julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

xen/drivers/passthrough/arm/Makefile

@@ -1 +1,2 @@
 obj-y += iommu.o
+obj-y += smmu.o