This adds device tree bindings for the IXP4xx V.35 WAN high
speed serial (HSS) link.

An example is added to the NPE example where the HSS appears
as a child.

Cc: devicetree@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>