[ARM] kirkwood: combine support for openrd base/client support

Inspired by the mach-ep93xx flattening work, there is really not
much difference between the OpenRD base and client board support
so they should be merged together.

Signed-off-by: Alexander Clouter <alex@digriz.org.uk>
Acked-by: Simon Kagstrom <simon.kagstrom@netinsight.net>
Signed-off-by: Nicolas Pitre <nico@fluxnic.net>