tracing/sched: Add sched_pi_setprio tracepoint

Add a tracepoint that shows the priority of a task being boosted
via priority inheritance.

Cc: Gregory Haskins <ghaskins@novell.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/sched.c b/kernel/sched.c
index 9ca8ad0..4ad4738 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4355,6 +4355,7 @@
 
 	rq = task_rq_lock(p, &flags);
 
+	trace_sched_pi_setprio(p, prio);
 	oldprio = p->prio;
 	prev_class = p->sched_class;
 	on_rq = p->se.on_rq;