iommu/vt-d: Add initial support for PASID tables

Add CONFIG_INTEL_IOMMU_SVM, and allocate PASID tables on supported hardware.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index d9da766..e3b2c2e 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -135,6 +135,14 @@
 	  and include PCI device scope covered by these DMA
 	  remapping devices.
 
+config INTEL_IOMMU_SVM
+	bool "Support for Shared Virtual Memory with Intel IOMMU"
+	depends on INTEL_IOMMU && X86
+	help
+	  Shared Virtual Memory (SVM) provides a facility for devices
+	  to access DMA resources through process address space by
+	  means of a Process Address Space ID (PASID).
+
 config INTEL_IOMMU_DEFAULT_ON
 	def_bool y
 	prompt "Enable Intel DMA Remapping Devices by default"