[ARM] Prevent "scheduling while atomic" in cpu_idle()

arch/arm/kernel/process.c

@@ -91,15 +91,16 @@ void default_idle(void)
 void cpu_idle(void)
 {
 	/* endless idle loop with no priority at all */
-	preempt_disable();
 	while (1) {
 		void (*idle)(void) = pm_idle;
 		if (!idle)
 			idle = default_idle;
+		preempt_disable();
 		leds_event(led_idle_start);
 		while (!need_resched())
 			idle();
 		leds_event(led_idle_end);
+		preempt_enable();
 		schedule();
 	}
 }