reboot: Make restart notifier API private

No users of the restart notifier API left, it's replaced with the sys-off
handler based API. Make old restart API private to kernel/reboot.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

include/linux/reboot.h

@@ -70,8 +70,6 @@ extern int unregister_reboot_notifier(struct notifier_block *);
 
 extern int devm_register_reboot_notifier(struct device *, struct notifier_block *);
 
-extern int register_restart_handler(struct notifier_block *);
-extern int unregister_restart_handler(struct notifier_block *);
 extern void do_kernel_restart(char *cmd);
 
 /*

kernel/reboot.c

@@ -173,7 +173,7 @@ static ATOMIC_NOTIFIER_HEAD(restart_handler_list);
  *	Currently always returns zero, as atomic_notifier_chain_register()
  *	always returns zero.
  */
-int register_restart_handler(struct notifier_block *nb)
+static int register_restart_handler(struct notifier_block *nb)
 {
 	int ret;
 
@@ -192,7 +192,6 @@ int register_restart_handler(struct notifier_block *nb)
 
 	return atomic_notifier_chain_register(&restart_handler_list, nb);
 }
-EXPORT_SYMBOL(register_restart_handler);
 
 /**
  *	unregister_restart_handler - Unregister previously registered
@@ -203,11 +202,10 @@ EXPORT_SYMBOL(register_restart_handler);
  *
  *	Returns zero on success, or %-ENOENT on failure.
  */
-int unregister_restart_handler(struct notifier_block *nb)
+static int unregister_restart_handler(struct notifier_block *nb)
 {
 	return atomic_notifier_chain_unregister(&restart_handler_list, nb);
 }
-EXPORT_SYMBOL(unregister_restart_handler);
 
 /**
  *	do_kernel_restart - Execute kernel restart handler call chain