rcu: Add rcutorture test for call_srcu()

Add srcu_torture_deferred_free() for srcu_ops so as to test the new
call_srcu().  Rename the original srcu_ops to srcu_sync_ops.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>