rcutorture: Make srcu_lockdep.sh check reader-conflict handling

Mixing different flavors of RCU readers is forbidden, for example, you
should not use srcu_read_lock() and srcu_read_lock_nmisafe() on the same
srcu_struct structure.  There are checks for this, but these checks are
not tested on a regular basis.  This commit therefore adds such tests
to srcu_lockdep.sh.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>