rcutorture: Abstract torture_shutdown()

Because auto-shutdown of torture testing is not specific to RCU,
this commit moves the auto-shutdown function to kernel/torture.c.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

include/linux/torture.h

@@ -72,8 +72,10 @@ unsigned long torture_random(struct torture_random_state *trsp);
 void torture_shuffle_task_register(struct task_struct *tp);
 int torture_shuffle_init(long shuffint);
 
-/* Shutdown task absorption, for when the tasks cannot safely be killed. */
+/* Test auto-shutdown handling. */
 void torture_shutdown_absorb(const char *title);
+int torture_shutdown_init(int ssecs, void (*cleanup)(void));
+void torture_shutdown_cleanup(void);
 
 /* Task stuttering, which forces load/no-load transitions. */
 void stutter_wait(const char *title);