srcu: Move rcu_scheduler_starting() from Tiny RCU to Tiny SRCU

Other than lockdep support, Tiny RCU has no need for the
scheduler status.  However, Tiny SRCU will need this to control
boot-time behavior independent of lockdep.  Therefore, this commit
moves rcu_scheduler_starting() from kernel/rcu/tiny_plugin.h to
kernel/rcu/srcutiny.c.  This in turn allows the complete removal of
kernel/rcu/tiny_plugin.h.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

include/linux/rcupdate.h

@@ -105,6 +105,7 @@ static inline int rcu_preempt_depth(void)
 
 /* Internal to kernel */
 void rcu_init(void);
+extern int rcu_scheduler_active __read_mostly;
 void rcu_sched_qs(void);
 void rcu_bh_qs(void);
 void rcu_check_callbacks(int user);