select IOMMU_API when DMAR and/or AMD_IOMMU is selected

These two IOMMUs can implement the current version of this API. So
select the API if one or both of these IOMMU drivers is selected.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 249d1e0..4737435 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -599,6 +599,9 @@
 config IOMMU_HELPER
 	def_bool (CALGARY_IOMMU || GART_IOMMU || SWIOTLB || AMD_IOMMU)
 
+config IOMMU_API
+	def_bool (AMD_IOMMU || DMAR)
+
 config MAXSMP
 	bool "Configure Maximum number of SMP Processors and NUMA Nodes"
 	depends on X86_64 && SMP && DEBUG_KERNEL && EXPERIMENTAL