ramips: add board alias for the ALL0239-3G

Generate image for the ALL0239-3G which can be flashed through the
chipset-vendor SDK based firmware's web-interface and bootloader.

The bootloader seems to ignore uImage checksum errors, but does complain about
them once the 0xDEADC0DE was replaced by an actual JFFS2 page.

I'm working on implementing fixtrx for uImage in the mtd package to solve this.

Signed-off-by: Daniel Golle <dgolle@allnet.de>

SVN-Revision: 33206