dt-bindings: display: rockchip-lvds: Declare PX30 compatible

Document the PX30 LVDS compatible.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20191224143900.23567-2-miquel.raynal@bootlin.com

Documentation/devicetree/bindings/display/rockchip/rockchip-lvds.txt

@@ -4,6 +4,7 @@ Rockchip RK3288 LVDS interface
 Required properties:
 - compatible: matching the soc type, one of
 	- "rockchip,rk3288-lvds";
+	- "rockchip,px30-lvds";
 
 - reg: physical base address of the controller and length
 	of memory mapped region.