Support for LinkStation / KuroBox HD and HG PPC models

This patch is based on the port by Mihai Georgian (see linkstation.c for
Copyright information) and implements support for LinkStation / KuroBox HD
and HG PPC models from Buffalo Technology, whereby HD is deactivated at
the moment, pending network driver fixing.

Notice to users: this is pretty much a barebone port. Support for network
on HG models is already in the U-Boot mainline, but you might also want
patches to switch fan / phy modes depending on the negotiated ethernet
parameters. This patch also doesn't support console switching, booting EM
mode, Buffalo specific ext2 magic number. So, if you want to use any of
those, you need additional patches. Otherwise this patche provides a fully
functional u-boot with a network console on your system.

Signed-off-by: Guennadi Liakhovetski <lg@denx.de>