arm: dts: visconti: Add DT support for Toshiba Visconti5 ethernet controller

Add the ethernet controller node in Toshiba Visconti5 SoC-specific DT file.
And enable this node in TMPV7708 RM main board's board-specific DT file.

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