The Intel IXP4xx SoCs have an expansion bus that is usually just
used for flash memory and configured by the boot loaders and can
be accessed using the "simple-bus".

However some devices need more elaborate configuration and then we
need to provide a proper 3-unit address space indicating chip
select for each device and provide timing and similar information.

Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>