cpuidle, ARM/imx6: Push RCU-idle into driver

Doing RCU-idle outside the driver, only to then temporarily enable it
again, at least twice, before going idle is suboptimal.

Notably both cpu_pm_enter() and cpu_cluster_pm_enter() implicity
re-enable RCU.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20230112195539.821714572@infradead.org

arch/arm/mach-imx/cpuidle-imx6sx.c

@@ -47,7 +47,9 @@ static int imx6sx_enter_wait(struct cpuidle_device *dev,
 		cpu_pm_enter();
 		cpu_cluster_pm_enter();
 
+		ct_idle_enter();
 		cpu_suspend(0, imx6sx_idle_finish);
+		ct_idle_exit();
 
 		cpu_cluster_pm_exit();
 		cpu_pm_exit();
@@ -87,7 +89,8 @@ static struct cpuidle_driver imx6sx_cpuidle_driver = {
 			 */
 			.exit_latency = 300,
 			.target_residency = 500,
-			.flags = CPUIDLE_FLAG_TIMER_STOP,
+			.flags = CPUIDLE_FLAG_TIMER_STOP |
+				 CPUIDLE_FLAG_RCU_IDLE,
 			.enter = imx6sx_enter_wait,
 			.name = "LOW-POWER-IDLE",
 			.desc = "ARM power off",