dt-bindings: display: Document Himax HX8394 panel rotation

Document panel rotation for Himax HX8394 display panel.
Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231204185719.569021-4-macroalpha82@gmail.comSigned-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231204185719.569021-4-macroalpha82@gmail.com

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

@@ -31,6 +31,8 @@ properties:
 
   backlight: true
 
+  rotation: true
+
   port: true
 
   vcc-supply: