string_choices: Add wrapper for str_down_up()

The string choice functions which are not clearly true/false synonyms
also have inverted wrappers. Add this for str_down_up() as well.
Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20240812182939.work.424-kees@kernel.orgReviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Kees Cook <kees@kernel.org>

include/linux/string_choices.h

@@ -46,6 +46,7 @@ static inline const char *str_up_down(bool v)
 {
 	return v ? "up" : "down";
 }
+#define str_down_up(v)		str_up_down(!(v))
 
 /**
  * str_plural - Return the simple pluralization based on English counts