dt-bindings: net: Add DT bindings for Toshiba Visconti TMPV7700 SoC

Add device tree bindings for ethernet controller of Toshiba Visconti
TMPV7700 SoC series.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>