ARM: dts: rockchip: add chosen node on veyron devices

In order to use earlycon, the stdout-path property needs to be set
in the chosen node. All veyron devices use uart2 for debugging, so
add it to the core veyron dtsi.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>