x86: move dma_*_coherent functions to include file

All the x86 DMA-API functions are defined in asm/dma-mapping.h. This patch
moves the dma_*_coherent functions also to this header file because they are
now small enough to do so.
This is done as a separate patch because it also includes some renaming and
restructuring of the dma-mapping.h file.

Signed-off-by: Joerg Roedel <joerg.roede@amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/pci-gart_64.c b/arch/x86/kernel/pci-gart_64.c
index ef753e2..e81df25 100644
--- a/arch/x86/kernel/pci-gart_64.c
+++ b/arch/x86/kernel/pci-gart_64.c
@@ -276,7 +276,7 @@
 	unsigned long bus;
 
 	if (!dev)
-		dev = &fallback_dev;
+		dev = &x86_dma_fallback_dev;
 
 	if (!need_iommu(dev, paddr, size))
 		return paddr;
@@ -427,7 +427,7 @@
 		return 0;
 
 	if (!dev)
-		dev = &fallback_dev;
+		dev = &x86_dma_fallback_dev;
 
 	out = 0;
 	start = 0;