arm64: dts: rockchip: hook up the px30-evb dsi display

Create the necessary display nodes to activate the Xingpeng XPP055C272
dsi display that can be found on the px30-evb.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Link: https://lore.kernel.org/r/20191209145301.5307-2-heiko@sntech.de