ARM: dts: ixp4xx: Add Gateworks Avila GW2348 device tree

This adds a device tree file for the Gateworks Avila GW2348 platform
supporting all the features of the in-kernel boardfiles.

There are more boards in the Avila family, but this is the one that
is supported out-of-the-box by the current boardfiles. Some extra
features have been folded in from the upstream OpenWrt sources,
such as proper ethernet setup for both ethernet ports.

More variants can be added based on this device tree. Some of those
have DSA switches, multiple LEDs, multiple serial ports and similar
and would need some more elaborate work.

Cc: Michael-Luke Jones <mlj28@cam.ac.uk>
Cc: Deepak Saxena <dsaxena@plexity.net>
Cc: Tom Billman <kernel@giantshoulderinc.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>