x86: move dma_sync_single_for_cpu to common header

i386 gets an empty function.

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/kernel/pci-base_32.c b/arch/x86/kernel/pci-base_32.c
index 9205304..dce03c8 100644
--- a/arch/x86/kernel/pci-base_32.c
+++ b/arch/x86/kernel/pci-base_32.c
@@ -35,6 +35,7 @@
 	.unmap_single = NULL,
 	.map_sg = pci32_dma_map_sg,
 	.unmap_sg = NULL,
+	.sync_single_for_cpu = NULL,
 };
 
 const struct dma_mapping_ops *dma_ops = &pci32_dma_ops;