dt-bindings: display: rockchip-dsi: add px30 compatible

The px30 SoC also uses a dw-mipi-dsi controller, so add the
compatible value for it.

changes in v5:
- rebased on top of 5.5-rc1
- merged with dsi timing change to prevent ordering conflicts
Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191209143130.4553-6-heiko@sntech.de

Documentation/devicetree/bindings/display/rockchip/dw_mipi_dsi_rockchip.txt

@@ -4,8 +4,10 @@ Rockchip specific extensions to the Synopsys Designware MIPI DSI
 Required properties:
 - #address-cells: Should be <1>.
 - #size-cells: Should be <0>.
-- compatible: "rockchip,rk3288-mipi-dsi", "snps,dw-mipi-dsi".
-	      "rockchip,rk3399-mipi-dsi", "snps,dw-mipi-dsi".
+- compatible: one of
+	"rockchip,px30-mipi-dsi", "snps,dw-mipi-dsi"
+	"rockchip,rk3288-mipi-dsi", "snps,dw-mipi-dsi"
+	"rockchip,rk3399-mipi-dsi", "snps,dw-mipi-dsi"
 - reg: Represent the physical address range of the controller.
 - interrupts: Represent the controller's interrupt to the CPU(s).
 - clocks, clock-names: Phandles to the controller's pll reference