rcu: Make expedited RCU CPU stall warnings respond to controls

The expedited RCU CPU stall warnings currently responds to neither the
panic_on_rcu_stall sysctl setting nor the rcupdate.rcu_cpu_stall_suppress
kernel boot parameter.  This commit therefore updates the expedited code
to respond to these two controls.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree_exp.h

@@ -428,6 +428,9 @@ static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
 		if (ret > 0 || sync_rcu_preempt_exp_done(rnp_root))
 			return;
 		WARN_ON(ret < 0);  /* workqueues should not be signaled. */
+		if (rcu_cpu_stall_suppress)
+			continue;
+		panic_on_rcu_stall();
 		pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
 		       rsp->name);
 		ndetected = 0;