rcu: Implement lockdep_rcu_enabled for !CONFIG_DEBUG_LOCK_ALLOC

Provide an implementation for debug_lockdep_rcu_enabled() when
CONFIG_DEBUG_LOCK_ALLOC is not enabled. This allows code to check
if rcu lockdep debugging is available without needing an extra
check if CONFIG_DEBUG_LOCK_ALLOC is enabled.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

include/linux/rcupdate.h

@@ -340,6 +340,11 @@ static inline int rcu_read_lock_any_held(void)
 	return !preemptible();
 }
 
+static inline int debug_lockdep_rcu_enabled(void)
+{
+	return 0;
+}
+
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 #ifdef CONFIG_PROVE_RCU