dt-bindings: net: Add bindings for National Instruments XGE netdev

This adds bindings for the NI XGE 1G/10G network device.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>