rcu: Use rcu_gp_kthread_wake() to wake up grace period kthreads

Commit abedf8e2 ("rcu: Use simple wait queues where possible in
rcutree") converts Tree RCU's wait queues to simple wait queues,
but it incorrectly reverts the commit 2aa792e6 ("rcu: Use
rcu_gp_kthread_wake() to wake up grace period kthreads").  This can
result in redundant self-wakeups.

This commit therefore replaces the simple wait-queue wakeups with
rcu_gp_kthread_wake(), thus avoiding the redundant wakeups.

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