dt-bindings: display: himax-hx8394: Add Powkiddy X55 panel

Add compatible string for the Powkiddy X55 panel.
Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231204185719.569021-6-macroalpha82@gmail.comSigned-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231204185719.569021-6-macroalpha82@gmail.com

Documentation/devicetree/bindings/display/panel/himax,hx8394.yaml

@@ -23,6 +23,7 @@ properties:
     items:
       - enum:
           - hannstar,hsd060bhw4
+          - powkiddy,x55-panel
       - const: himax,hx8394
 
   reg: true