sched/headers: Prepare for new header dependencies before moving code to <linux/sched/debug.h>

We are going to split <linux/sched/debug.h> out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.

Create a trivial placeholder <linux/sched/debug.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.

Include the new header in the files that are going to need it.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/rcu/tree.c

@@ -35,6 +35,7 @@
 #include <linux/rcupdate_wait.h>
 #include <linux/interrupt.h>
 #include <linux/sched.h>
+#include <linux/sched/debug.h>
 #include <linux/nmi.h>
 #include <linux/atomic.h>
 #include <linux/bitops.h>

kernel/rcu/tree_plugin.h

@@ -27,6 +27,7 @@
 #include <linux/delay.h>
 #include <linux/gfp.h>
 #include <linux/oom.h>
+#include <linux/sched/debug.h>
 #include <linux/smpboot.h>
 #include <uapi/linux/sched/types.h>
 #include "../time/tick-internal.h"

kernel/rcu/update.c

@@ -37,6 +37,7 @@
 #include <linux/smp.h>
 #include <linux/interrupt.h>
 #include <linux/sched/signal.h>
+#include <linux/sched/debug.h>
 #include <linux/atomic.h>
 #include <linux/bitops.h>
 #include <linux/percpu.h>