x86: move dma_unmap_single to common header

i386 base does not need it, so it 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 d320244..bb0378f 100644
--- a/include/asm-x86/dma-mapping.h
+++ b/include/asm-x86/dma-mapping.h
@@ -66,4 +66,14 @@
 	return dma_ops->map_single(hwdev, ptr, size, direction);
 }
 
+static inline void
+dma_unmap_single(struct device *dev, dma_addr_t addr, size_t size,
+		 int direction)
+{
+	BUG_ON(!valid_dma_direction(direction));
+	if (dma_ops->unmap_single)
+		dma_ops->unmap_single(dev, addr, size, direction);
+}
+
+
 #endif