korad-kaxxxxp: prepare more versatile ID response text checks

Add more quirks for IDN responses: Some devices would not report the
vendor in their response. Some devices suffer from trailing garbage.
Move IDN response text checks to a new model_matches() routine, stick
with the strcmp() implementation in this commit for compatibility.

This commit does not change the set of supported models, but prepares
the addition of more versatile IDN response checks in a future version.