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

We are going to split <linux/sched/hotplug.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/hotplug.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/cpu.c

@@ -8,6 +8,7 @@
 #include <linux/init.h>
 #include <linux/notifier.h>
 #include <linux/sched/signal.h>
+#include <linux/sched/hotplug.h>
 #include <linux/unistd.h>
 #include <linux/cpu.h>
 #include <linux/oom.h>

kernel/sched/core.c

@@ -9,6 +9,7 @@
 #include <linux/sched/clock.h>
 #include <uapi/linux/sched/types.h>
 #include <linux/sched/loadavg.h>
+#include <linux/sched/hotplug.h>
 #include <linux/cpuset.h>
 #include <linux/delayacct.h>
 #include <linux/init_task.h>

kernel/sched/sched.h

@@ -3,6 +3,7 @@
 #include <linux/sched/sysctl.h>
 #include <linux/sched/topology.h>
 #include <linux/sched/rt.h>
+#include <linux/sched/deadline.h>
 #include <linux/sched/clock.h>
 #include <linux/sched/wake_q.h>
 #include <linux/sched/signal.h>
@@ -12,8 +13,9 @@
 #include <linux/sched/stat.h>
 #include <linux/sched/nohz.h>
 #include <linux/sched/debug.h>
+#include <linux/sched/hotplug.h>
+
 #include <linux/u64_stats_sync.h>
-#include <linux/sched/deadline.h>
 #include <linux/kernel_stat.h>
 #include <linux/binfmts.h>
 #include <linux/mutex.h>