dt-bindings: ARM: dts: rockchip: Add bindings for rk3288-veyron-mighty

Mighty is basically the same Chromebook as Jaq but it has a full-sized
SD slot and some different (slightly more rugged) plastics around it.
Like Jaq, Mighty may show up with various different brandings but all
of them have the same board inside.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>