dt-bindings: arm: toshiba: add Toshiba Visconti ARM SoCs

Add device tree bindings for the Toshiba Visconti ARM SoCs.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Reviewed-by: Punit Agrawal <punit1.agrawal@toshiba.co.jp>
Reviewed-by: Rob Herring <robh@kernel.org>