ARM: initial DTS support for km_kirkwood

This is a first attempt to support the km_kirkwood reference design with
a device tree. This km_kirkwood design is present in many Keymile
products. It is based on the Marvell Bobcat SOC which integrates a
Kirkwood CPU next to a big L2 Ethernet Switch. The Kirkwood in the SOC
is very similar to the "normal" one, but there are a few differences.

This initial support is minimal: the kernel can boot with network
(ge0), serial port and NAND functional.

Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Cc: Holger Brunck <holger.brunck@keymile.com>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>