ARM: dts: ixp4xx: Add devicetree for Netgear WG302v2

This adds a devicetree for the Netgear WG302v2 router.

The DTS is mostly based on the upstream boardfile but I also
added in the ethernet from OpenWrt to get a more complete
system.

Cc: Imre Kaloz <kaloz@openwrt.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>