Currently we build factory images only for DGS-1210-28 model. Relax
that constraint and take care about all models. Tested on DGS-1210-20
and should work on other models too because of common flash layout.
Tested-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>