x86: reduce forbid_dac's visibility

It's not used anywhere outside its declaring file.
Signed-off-by: NJan Beulich <jbeulich@novell.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/pci-dma.c

@@ -9,8 +9,7 @@
 #include <asm/calgary.h>
 #include <asm/amd_iommu.h>
 
-int forbid_dac __read_mostly;
-EXPORT_SYMBOL(forbid_dac);
+static int forbid_dac __read_mostly;
 
 const struct dma_mapping_ops *dma_ops;
 EXPORT_SYMBOL(dma_ops);

include/asm-x86/dma-mapping.h

@@ -14,7 +14,6 @@ extern dma_addr_t bad_dma_address;
 extern int iommu_merge;
 extern struct device fallback_dev;
 extern int panic_on_overflow;
-extern int forbid_dac;
 extern int force_iommu;
 
 struct dma_mapping_ops {