iommu/arm-smmu: Add support for MSI on SMMUv3

Despite being a platform device, the SMMUv3 is capable of signaling
interrupts using MSIs. Hook it into the platform MSI framework and
enjoy faults being reported in a new and exciting way.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
[will: tidied up the binding example and reworked most of the code]
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index d9da766..cc2dfa5 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -362,6 +362,7 @@
 	depends on ARM64 && PCI
 	select IOMMU_API
 	select IOMMU_IO_PGTABLE_LPAE
+	select GENERIC_MSI_IRQ_DOMAIN
 	help
 	  Support for implementations of the ARM System MMU architecture
 	  version 3 providing translation support to a PCIe root complex.