torture: Add --do-{,no-}normal to torture.sh

Right now, torture.sh runs normal runs unconditionally, which can be slow
and thus annoying when you only want to test --kcsan or --kasan runs.
This commit therefore adds a --do-normal argument so that "--kcsan
--do-no-kasan --do-no-normal" runs only KCSAN runs.  Note that specifying
"--do-no-kasan --do-no-kcsan --do-no-normal" gets normal runs, so you
should not try to use this as a synonym for --do-none.

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