torture: Rename SRCU-t and SRCU-u to avoid lowercase characters

The convention that scenario names are all uppercase has two exceptions,
SRCU-t and SRCU-u.  This commit therefore renames them to SRCU-T and
SRCU-U, respectively, to bring them in line with this convention.  This in
turn permits tighter argument checking in the torture-test scripting.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/testing/selftests/rcutorture/configs/rcu/CFLIST

@@ -7,8 +7,8 @@ TREE07
 TREE09
 SRCU-N
 SRCU-P
-SRCU-t
-SRCU-u
+SRCU-T
+SRCU-U
 TINY01
 TINY02
 TASKS01