sched/rt: Document scheduler related skip-resched-check sites

Create a distinction between scheduler related preempt_enable_no_resched()
calls and the nearly one hundred other places in the kernel that do not
want to reschedule, for one reason or another.

This distinction matters for -rt, where the scheduler and the non-scheduler
preempt models (and checks) are different. For upstream it's purely
documentational.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/n/tip-gs88fvx2mdv5psnzxnv575ke@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/powerpc/kernel/idle.c

@@ -102,7 +102,7 @@ void cpu_idle(void)
 		rcu_idle_exit();
 		tick_nohz_idle_exit();
 		if (cpu_should_die()) {
-			preempt_enable_no_resched();
+			sched_preempt_enable_no_resched();
 			cpu_die();
 		}
 		schedule_preempt_disabled();