sched/headers: Prepare to move _init() prototypes from <linux/sched.h> to <linux/sched/init.h>

But first introduce a trivial header and update usage sites.
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/ia64/kernel/setup.c

@@ -29,6 +29,7 @@
 #include <linux/bootmem.h>
 #include <linux/console.h>
 #include <linux/delay.h>
+#include <linux/cpu.h>
 #include <linux/kernel.h>
 #include <linux/reboot.h>
 #include <linux/sched.h>

arch/m32r/kernel/traps.c

@@ -17,6 +17,7 @@
 #include <linux/sched/debug.h>
 #include <linux/sched/task_stack.h>
 #include <linux/mm.h>
+#include <linux/cpu.h>
 
 #include <asm/page.h>
 #include <asm/processor.h>

arch/s390/kernel/setup.c

@@ -19,6 +19,7 @@
 #include <linux/export.h>
 #include <linux/sched.h>
 #include <linux/sched/task.h>
+#include <linux/cpu.h>
 #include <linux/kernel.h>
 #include <linux/memblock.h>
 #include <linux/mm.h>

include/linux/cpu.h

@@ -30,6 +30,8 @@ struct cpu {
 
 extern void boot_cpu_init(void);
 extern void boot_cpu_state_init(void);
+extern void cpu_init(void);
+extern void trap_init(void);
 
 extern int register_cpu(struct cpu *cpu, int num);
 extern struct device *get_cpu_device(unsigned cpu);

include/linux/sched/init.h

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

init/main.c

@@ -63,6 +63,7 @@
 #include <linux/device.h>
 #include <linux/kthread.h>
 #include <linux/sched.h>
+#include <linux/sched/init.h>
 #include <linux/signal.h>
 #include <linux/idr.h>
 #include <linux/kgdb.h>

kernel/sched/sched.h

@@ -18,6 +18,7 @@
 #include <linux/sched/task.h>
 #include <linux/sched/task_stack.h>
 #include <linux/sched/cputime.h>
+#include <linux/sched/init.h>
 
 #include <linux/u64_stats_sync.h>
 #include <linux/kernel_stat.h>