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 <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>

arch/x86/include/asm/mwait.h

@@ -2,6 +2,7 @@
 #define _ASM_X86_MWAIT_H
 
 #include <linux/sched.h>
+#include <linux/sched/idle.h>
 
 #include <asm/cpufeature.h>
 

arch/x86/kernel/process.c

@@ -7,6 +7,7 @@
 #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

@@ -11,6 +11,7 @@
 #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

@@ -3,4 +3,6 @@
 
 #include <linux/sched.h>
 
+#include <linux/sched/idle.h>
+
 #endif /* _LINUX_SCHED_TOPOLOGY_H */

kernel/sched/idle.c

@@ -2,6 +2,7 @@
  * 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

@@ -17,6 +17,7 @@
 #include <linux/smp.h>
 #include <linux/cpu.h>
 #include <linux/sched.h>
+#include <linux/sched/idle.h>
 #include <linux/hypervisor.h>
 
 #include "smpboot.h"