IA64: fix compile error on IA64_DIG_VTD

This moves iommu_detected to arch/ia64/kernel/dma-mapping.c from
arch/ia64/kernel/pci-swiotlb.c to fix the following error on on
IA64_DIG_VTD:

 arch/ia64/kernel/built-in.o: In function `pci_iommu_init':
 pci-dma.c:(.init.text+0xa021): undefined reference to `iommu_detected'
 pci-dma.c:(.init.text+0xa030): undefined reference to `iommu_detected'
 drivers/built-in.o: In function `detect_intel_iommu':
 (.init.text+0x11c0): undefined reference to `iommu_detected'
 drivers/built-in.o: In function `detect_intel_iommu':
 (.init.text+0x11e1): undefined reference to `iommu_detected'

iommu_detected is used to handle IOMMUs so I guess that
arch/ia64/kernel/dma-mapping.c is ok (there might be a better place
for it though).

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/ia64/kernel/dma-mapping.c b/arch/ia64/kernel/dma-mapping.c
index 7060e13..086a2ae 100644
--- a/arch/ia64/kernel/dma-mapping.c
+++ b/arch/ia64/kernel/dma-mapping.c
@@ -1,5 +1,8 @@
 #include <linux/dma-mapping.h>
 
+/* Set this to 1 if there is a HW IOMMU in the system */
+int iommu_detected __read_mostly;
+
 struct dma_map_ops *dma_ops;
 EXPORT_SYMBOL(dma_ops);