bcm53xx: build factory images for WZR-900DHP series

only factory images for DHP-EU and DHP2-JP (fw ver. 2.x) are built.

this will not work for DHP-JP/AP/TW (fw ver. 1.x) because they use
different buffalo_csum() formula.

Signed-off-by: FUKAUMI Naoki <naobsd@gmail.com>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>