rcutorture: Test early boot call_srcu()

Now that SRCU permits call_srcu() to be invoked at early boot, this
commit ensures that the rcutorture scripting tests early boot call_srcu().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

tools/testing/selftests/rcutorture/configs/rcu/SRCU-P.boot

 rcutorture.torture_type=srcud
+rcupdate.rcu_self_test=1

tools/testing/selftests/rcutorture/configs/rcu/SRCU-u.boot

 rcutorture.torture_type=srcud
+rcupdate.rcu_self_test=1

tools/testing/selftests/rcutorture/configs/rcu/TREE05.boot

@@ -3,3 +3,4 @@ rcupdate.rcu_self_test_sched=1
 rcutree.gp_preinit_delay=3
 rcutree.gp_init_delay=3
 rcutree.gp_cleanup_delay=3
+rcupdate.rcu_self_test=1