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>

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);