lantiq: use the compatible string as board name

lantiq: use the compatible string as board name

Use the first compatible string as board name in userspace. Add the new
board name as well as the former used board name to the image metadata
to keep compatibilty with already deployed installations.

Don't add the former used boardname for boards which exists only in
master or evaluation boards.

Signed-off-by: Mathias Kresin <dev@kresin.me>