lib/string_helpers: Add str_read_write() helper

Add str_read_write() helper to return 'read' or 'write' string literal.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Dmitry Rokosov <ddrokosov@sberdevices.ru>
Link: https://lore.kernel.org/r/20220822175011.2886-2-ddrokosov@sberdevices.ruSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

include/linux/string_helpers.h

@@ -126,4 +126,9 @@ static inline const char *str_enabled_disabled(bool v)
 	return v ? "enabled" : "disabled";
 }
 
+static inline const char *str_read_write(bool v)
+{
+	return v ? "read" : "write";
+}
+
 #endif