[SPARC64]: Add basic infrastructure for MD add/remove notification.

And add dummy handlers for the VIO device layer.  These will be filled
in with real code after the vdc, vnet, and ds drivers are reworked to
have simpler dependencies on the VIO device tree.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/asm-sparc64/mdesc.h b/include/asm-sparc64/mdesc.h
index e97c431..1acc727 100644
--- a/include/asm-sparc64/mdesc.h
+++ b/include/asm-sparc64/mdesc.h
@@ -61,6 +61,16 @@
 
 extern void mdesc_update(void);
 
+struct mdesc_notifier_client {
+	void (*add)(struct mdesc_handle *handle, u64 node);
+	void (*remove)(struct mdesc_handle *handle, u64 node);
+
+	const char			*node_name;
+	struct mdesc_notifier_client	*next;
+};
+
+extern void mdesc_register_notifier(struct mdesc_notifier_client *client);
+
 extern void mdesc_fill_in_cpu_data(cpumask_t mask);
 
 extern void sun4v_mdesc_init(void);