Replace swiotlb extern with include

Signed-off-by: Andi Kleen <ak@suse.de>

Index: linux/arch/x86_64/mm/init.c
===================================================================
--- linux.orig/arch/x86_64/mm/init.c
+++ linux/arch/x86_64/mm/init.c
@@ -22,6 +22,7 @@
 #include <linux/pagemap.h>
 #include <linux/bootmem.h>
 #include <linux/proc_fs.h>
+#include <linux/pci.h>
 
 #include <asm/processor.h>
 #include <asm/system.h>
@@ -42,10 +43,6 @@
 #define Dprintk(x...)
 #endif
 
-#ifdef CONFIG_GART_IOMMU
-extern int swiotlb;
-#endif
-
 static unsigned long dma_reserve __initdata;
 
 DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);