rcu: Consolidate rcu_synchronize and wakeme_after_rcu()

There are currently duplicate identical definitions of the
rcu_synchronize() structure and the wakeme_after_rcu() function.
Thie commit therefore consolidates them.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

include/linux/rcupdate.h

@@ -195,6 +195,15 @@ void call_rcu_sched(struct rcu_head *head,
 
 void synchronize_sched(void);
 
+/*
+ * Structure allowing asynchronous waiting on RCU.
+ */
+struct rcu_synchronize {
+	struct rcu_head head;
+	struct completion completion;
+};
+void wakeme_after_rcu(struct rcu_head *head);
+
 /**
  * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
  * @head: structure to be used for queueing the RCU updates.