rcutorture: Make torture.sh refscale and rcuscale specify Tasks Trace RCU

Now that the Tasks RCU flavors are selected by their users rather than
by the rcutorture scenarios, torture.sh fails when attempting to run
NOPREEMPT scenarios for refscale and rcuscale.  This commit therefore
makes torture.sh specify CONFIG_TASKS_TRACE_RCU=y to avoid such failure.

Why not also CONFIG_TASKS_RCU?  Because tracing selects this one.

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