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/include/asm-x86/dma-mapping.h b/include/asm-x86/dma-mapping.h
index 6e7747a..507069d 100644
--- a/include/asm-x86/dma-mapping.h
+++ b/include/asm-x86/dma-mapping.h
@@ -91,4 +91,16 @@
 	if (dma_ops->unmap_sg)
 		dma_ops->unmap_sg(hwdev, sg, nents, direction);
 }
+
+static inline void
+dma_sync_single_for_cpu(struct device *hwdev, dma_addr_t dma_handle,
+			size_t size, int direction)
+{
+	BUG_ON(!valid_dma_direction(direction));
+	if (dma_ops->sync_single_for_cpu)
+		dma_ops->sync_single_for_cpu(hwdev, dma_handle, size,
+					     direction);
+	flush_write_buffers();
+}
+
 #endif