ARM: imx6q: Fixup RCU usage for cpuidle

The commit eb1f0023 ("lockdep,trace: Expose tracepoints"), started to
expose us for tracepoints. For imx6q cpuidle, this leads to an RCU splat
according to below.

[6.870684] [<c0db7690>] (_raw_spin_lock) from [<c011f6a4>] (imx6q_enter_wait+0x18/0x9c)
[6.878846] [<c011f6a4>] (imx6q_enter_wait) from [<c09abfb0>] (cpuidle_enter_state+0x168/0x5e4)

To fix the problem, let's assign the corresponding idlestate->flags the
CPUIDLE_FLAG_RCU_IDLE bit, which enables us to call rcu_idle_enter|exit()
at the proper point.
Reported-by: Dong Aisheng <aisheng.dong@nxp.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

arch/arm/mach-imx/cpuidle-imx6q.c

@@ -24,7 +24,9 @@ static int imx6q_enter_wait(struct cpuidle_device *dev,
 		imx6_set_lpm(WAIT_UNCLOCKED);
 	raw_spin_unlock(&cpuidle_lock);
 
+	rcu_idle_enter();
 	cpu_do_idle();
+	rcu_idle_exit();
 
 	raw_spin_lock(&cpuidle_lock);
 	if (num_idle_cpus-- == num_online_cpus())
@@ -44,7 +46,7 @@ static struct cpuidle_driver imx6q_cpuidle_driver = {
 		{
 			.exit_latency = 50,
 			.target_residency = 75,
-			.flags = CPUIDLE_FLAG_TIMER_STOP,
+			.flags = CPUIDLE_FLAG_TIMER_STOP | CPUIDLE_FLAG_RCU_IDLE,
 			.enter = imx6q_enter_wait,
 			.name = "WAIT",
 			.desc = "Clock off",