I can't tell you why this is happening. The kernel should support this device, but I've got none to test. It did in the past so I don't see why suddenly the support would be broken now and other devices are fine.
Try new U-Boot version, maybe you will have more luck with that
http://mirror.archlinuxarm.org/arm/alar ... pkg.tar.xz
Use kwboot to send uboot image to the device and see if it boots (without actually flashing the uboot).
There is a caveat with this uboot: there is no MAC address assigned to the NIC, so you won't be able to bring it up until you assign it manually: viewtopic.php?f=53&t=8857&start=40#p48186