ARM: dts: ixp4xx: Add devicetree for Iomega NAS 100D

This creates a more or less fully featured device tree for the
IXP42x-based Iomega NAS 100D.

We can't read out the raw flash contents for ethernet MAC, and
we cannot handle a power-off-button inside the kernel like the
boardfile does. These two things are normally done in userspace.

This conversion is part of moving all of the IXP4xx board files
over to device tree to modernize the IXP4xx kernel.

Cc: Rod Whitby <rod@whitby.id.au>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>