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/sparc/kernel/process_64.c

@@ -106,7 +106,7 @@ void cpu_idle(void)
 
 #ifdef CONFIG_HOTPLUG_CPU
 		if (cpu_is_offline(cpu)) {
-			preempt_enable_no_resched();
+			sched_preempt_enable_no_resched();
 			cpu_play_dead();
 		}
 #endif