sched/headers: Simplify and clean up header usage in the scheduler

Do the following cleanups and simplifications:

 - sched/sched.h already includes <asm/paravirt.h>, so no need to
   include it in sched/core.c again.

 - order the <linux/sched/*.h> headers alphabetically

 - add all <linux/sched/*.h> headers to kernel/sched/sched.h

 - remove all unnecessary includes from the .c files that
   are already included in kernel/sched/sched.h.

Finally, make all scheduler .c files use a single common header:

  #include "sched.h"

... which now contains a union of the relied upon headers.

This makes the various .c files easier to read and easier to handle.

Cc: 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/kernel/sched/debug.c b/kernel/sched/debug.c
index 7c82a9b..644d9a4 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -1,7 +1,7 @@
 /*
  * kernel/sched/debug.c
  *
- * Print the CFS rbtree
+ * Print the CFS rbtree and other debugging details
  *
  * Copyright(C) 2007, Red Hat, Inc., Ingo Molnar
  *
@@ -9,15 +9,6 @@
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  */
-#include <linux/proc_fs.h>
-#include <linux/sched/mm.h>
-#include <linux/sched/task.h>
-#include <linux/seq_file.h>
-#include <linux/kallsyms.h>
-#include <linux/utsname.h>
-#include <linux/mempolicy.h>
-#include <linux/debugfs.h>
-
 #include "sched.h"
 
 static DEFINE_SPINLOCK(sched_debug_lock);