iommu/core: Fix build with INTR_REMAP=y && CONFIG_DMAR=n

IOMMU_API is not selected when no DMA remapping driver is
selected, but the whole drivers/iommu/ directory is only
built with IOMMU_API=y. Fixed with this patch by including
the directory with IOMMU_SUPPORT instead.
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

drivers/Makefile

@@ -122,4 +122,4 @@ obj-y				+= ieee802154/
 obj-y				+= clk/
 
 obj-$(CONFIG_HWSPINLOCK)	+= hwspinlock/
-obj-$(CONFIG_IOMMU_API)		+= iommu/
+obj-$(CONFIG_IOMMU_SUPPORT)	+= iommu/