dt-bindings: arm: rockchip: Add Powkiddy X55

The Powkiddy X55 is a handheld gaming device made by Powkiddy and
powered by the Rockchip RK3566 SoC. This device is somewhat similar
to the existing Powkiddy RK3566 devices, which have been grouped
together with a previous commit[1].

[1] https://lore.kernel.org/linux-rockchip/20231117202536.1387815-1-macroalpha82@gmail.com/T/#m4764997cfafaca22fe677200de96caa5fb8f0005Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231204185719.569021-10-macroalpha82@gmail.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip.yaml

@@ -675,6 +675,7 @@ properties:
           - enum:
               - powkiddy,rgb30
               - powkiddy,rk2023
+              - powkiddy,x55
           - const: rockchip,rk3566
 
       - description: Radxa Compute Module 3(CM3)