dt-bindings: display: add rotation property to sitronix,st7789v

The sitronix-st7789v driver now considers the rotation property.
Add the property to the documentation.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Michael Riesch <michael.riesch@wolfvision.net>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230718-feature-st7789v-v3-3-157d68fb63e2@wolfvision.net

Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml

@@ -25,6 +25,7 @@ properties:
   power-supply: true
   backlight: true
   port: true
+  rotation: true
 
   spi-cpha: true
   spi-cpol: true
@@ -58,6 +59,7 @@ examples:
             reset-gpios = <&pio 6 11 GPIO_ACTIVE_LOW>;
             backlight = <&pwm_bl>;
             power-supply = <&power>;
+            rotation = <180>;
             spi-max-frequency = <100000>;
             spi-cpol;
             spi-cpha;