lib/string_choices: Add str_true_false()/str_false_true() helper

Add str_true_false()/str_false_true() helper to return "true" or
"false" string literal.
Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Link: https://lore.kernel.org/r/20240827024517.914100-2-lihongbo22@huawei.comSigned-off-by: Kees Cook <kees@kernel.org>

include/linux/string_choices.h

@@ -48,6 +48,12 @@ static inline const char *str_up_down(bool v)
 }
 #define str_down_up(v)		str_up_down(!(v))
 
+static inline const char *str_true_false(bool v)
+{
+	return v ? "true" : "false";
+}
+#define str_false_true(v)		str_true_false(!(v))
+
 /**
  * str_plural - Return the simple pluralization based on English counts
  * @num: Number used for deciding pluralization