kcsan: Make strict mode imply interruptible watchers

If CONFIG_KCSAN_STRICT=y, select CONFIG_KCSAN_INTERRUPT_WATCHER as well.

With interruptible watchers, we'll also report same-CPU data races; if
we requested strict mode, we might as well show these, too.

Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>