printk: Add printk_deferred_once

Two of the three prink_deferred uses are really printk_once style
uses, so add a printk_deferred_once macro to simplify those call
sites.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Bohac <jbohac@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 5d7667b..b3512f1 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -890,14 +890,8 @@
 		 * but accrue some time due to boosting.
 		 */
 		if (likely(rt_b->rt_runtime)) {
-			static bool once = false;
-
 			rt_rq->rt_throttled = 1;
-
-			if (!once) {
-				once = true;
-				printk_deferred("sched: RT throttling activated\n");
-			}
+			printk_deferred_once("sched: RT throttling activated\n");
 		} else {
 			/*
 			 * In case we did anyway, make it go away,