torture: Reduce #ifdefs for preempt_schedule()

This commit adds a torture_preempt_schedule() that is nothingness
in !PREEMPT builds and is preempt_schedule() otherwise.  Then
torture_preempt_schedule() is used to eliminate several ugly #ifdefs,
both in rcutorture and in locktorture.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 74f6b01..e7d3cce 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -315,11 +315,9 @@ static void rcu_read_delay(struct torture_random_state *rrsp)
 	}
 	if (!(torture_random(rrsp) % (nrealreaders * 2 * shortdelay_us)))
 		udelay(shortdelay_us);
-#ifdef CONFIG_PREEMPT
 	if (!preempt_count() &&
 	    !(torture_random(rrsp) % (nrealreaders * 20000)))
-		preempt_schedule();  /* No QS if preempt_disable() in effect */
-#endif
+		torture_preempt_schedule();  /* QS only if preemptible. */
 }
 
 static void rcu_torture_read_unlock(int idx) __releases(RCU)