[POWERPC] iSeries: We need vio_enable_interrupts

Commit 3d0e91f7ace12499c4b00088e9a6b1361e1bb0ca introduced a requirement
for vio_enable_interrupts which iSeires has never needed.  So create a
dummy one.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/include/asm-powerpc/vio.h b/include/asm-powerpc/vio.h
index 0117b54..3a0975e 100644
--- a/include/asm-powerpc/vio.h
+++ b/include/asm-powerpc/vio.h
@@ -80,6 +80,11 @@
 extern struct vio_dev *vio_find_node(struct device_node *vnode);
 extern int vio_enable_interrupts(struct vio_dev *dev);
 extern int vio_disable_interrupts(struct vio_dev *dev);
+#else
+static inline int vio_enable_interrupts(struct vio_dev *dev)
+{
+	return 0;
+}
 #endif
 
 static inline struct vio_driver *to_vio_driver(struct device_driver *drv)