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

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

Create a trivial placeholder <linux/sched/clock.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>
diff --git a/lib/plist.c b/lib/plist.c
index 3a30c53..199408f 100644
--- a/lib/plist.c
+++ b/lib/plist.c
@@ -175,6 +175,7 @@
 
 #ifdef CONFIG_DEBUG_PI_LIST
 #include <linux/sched.h>
+#include <linux/sched/clock.h>
 #include <linux/module.h>
 #include <linux/init.h>