rcutorture: Add lockdep to one of the SRCU scenarios

Back when SRCU was simpler, there wasn't much need for lockdep.
However, with Tree SRCU, it is needed.  This commit therefore adds
CONFIG_PROVE_LOCKING to the SRCU-P scenario.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>