x86, gart: Rename pci-gart_64.c to amd_gart_64.c

This file only contains code relevant for the northbridge
gart in AMD processors. This patch renames the file to
represent this fact in the filename.
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

Documentation/x86/x86_64/boot-options.txt

@@ -206,7 +206,7 @@ IOMMU (input/output memory management unit)
       (e.g. because you have < 3 GB memory).
       Kernel boot message: "PCI-DMA: Disabling IOMMU"
 
-   2. <arch/x86_64/kernel/pci-gart.c>: AMD GART based hardware IOMMU.
+   2. <arch/x86/kernel/amd_gart_64.c>: AMD GART based hardware IOMMU.
       Kernel boot message: "PCI-DMA: using GART IOMMU"
 
    3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used

arch/x86/kernel/Makefile

@@ -117,7 +117,7 @@ obj-$(CONFIG_OF)			+= devicetree.o
 ifeq ($(CONFIG_X86_64),y)
 	obj-$(CONFIG_AUDIT)		+= audit_64.o
 
-	obj-$(CONFIG_GART_IOMMU)	+= pci-gart_64.o aperture_64.o
+	obj-$(CONFIG_GART_IOMMU)	+= amd_gart_64.o aperture_64.o
 	obj-$(CONFIG_CALGARY_IOMMU)	+= pci-calgary_64.o tce_64.o
 	obj-$(CONFIG_AMD_IOMMU)		+= amd_iommu_init.o amd_iommu.o