rcutorture: Adjust scenarios SRCU-t and SRCU-u to make kconfig happy

The SRCU-u scenario expects to enable lockdep but to also disable the
CONFIG_PREEMPT_COUNT kconfig option.  This no longer works.  This commit
therefore instead enables lockdep in SRCU-t, which then allows SRCU-u
to disable CONFIG_PREEMPT_COUNT.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>