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

We are going to split <linux/sched/idle.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/idle.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 <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/include/asm/mwait.h

···
 #define _ASM_X86_MWAIT_H
 
 #include <linux/sched.h>
+#include <linux/sched/idle.h>
 
 #include <asm/cpufeature.h>
 

arch/x86/kernel/process.c

···
 #include <linux/prctl.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
+#include <linux/sched/idle.h>
 #include <linux/init.h>
 #include <linux/export.h>
 #include <linux/pm.h>

drivers/cpuidle/driver.c

···
 #include <linux/mutex.h>
 #include <linux/module.h>
 #include <linux/sched.h>
+#include <linux/sched/idle.h>
 #include <linux/cpuidle.h>
 #include <linux/cpumask.h>
 #include <linux/tick.h>

include/linux/sched/idle.h

···
+#ifndef _LINUX_SCHED_IDLE_H
+#define _LINUX_SCHED_IDLE_H
+
+#include <linux/sched.h>
+
+#endif /* _LINUX_SCHED_IDLE_H */

include/linux/sched/topology.h

···
 
 #include <linux/sched.h>
 
+#include <linux/sched/idle.h>
+
 #endif /* _LINUX_SCHED_TOPOLOGY_H */

kernel/sched/idle.c

···
  * Generic entry point for the idle threads
  */
 #include <linux/sched.h>
+#include <linux/sched/idle.h>
 #include <linux/cpu.h>
 #include <linux/cpuidle.h>
 #include <linux/cpuhotplug.h>

kernel/smp.c

···
 #include <linux/smp.h>
 #include <linux/cpu.h>
 #include <linux/sched.h>
+#include <linux/sched/idle.h>
 #include <linux/hypervisor.h>
 
 #include "smpboot.h"