rcu: Do not include rtmutex_common.h unconditionally

This commit adjusts include files and provides definitions in preparation
for suppressing lockdep false-positive ->boost_mtx complaints.  Without
this preparation, architectures not supporting rt_mutex will get build
failures.
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree_plugin.h

@@ -54,6 +54,7 @@ DEFINE_PER_CPU(char, rcu_cpu_has_work);
  * This probably needs to be excluded from -rt builds.
  */
 #define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })
+#define rt_mutex_futex_unlock(x) WARN_ON_ONCE(1)
 
 #endif /* #else #ifdef CONFIG_RCU_BOOST */
 
@@ -911,8 +912,6 @@ void exit_rcu(void)
 
 #ifdef CONFIG_RCU_BOOST
 
-#include "../locking/rtmutex_common.h"
-
 static void rcu_wake_cond(struct task_struct *t, int status)
 {
 	/*