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/ia64/Kconfig b/arch/ia64/Kconfig
index 7fa8f61..3d31636 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -687,3 +687,6 @@
 
 config IOMMU_HELPER
 	def_bool (IA64_HP_ZX1 || IA64_HP_ZX1_SWIOTLB || IA64_GENERIC || SWIOTLB)
+
+config IOMMU_API
+	def_bool (DMAR)