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

Add compatible string for the Powkiddy X55 panel.

Signed-off-by: Chris Morgan <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Neil Armstrong <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

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

···
     items:
       - enum:
           - hannstar,hsd060bhw4
+          - powkiddy,x55-panel
       - const: himax,hx8394
 
   reg: true