dt-bindings: serial: snps-dw-apb-uart: include rs485 schema

The dw-apb-uart also can emulate rs485, so include the rs485
schema to allow validating rs485 properties.
Signed-off-by: Heiko Stuebner <heiko.stuebner@cherry.de>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231201140542.323564-1-heiko@sntech.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml

@@ -11,6 +11,7 @@ maintainers:
 
 allOf:
   - $ref: serial.yaml#
+  - $ref: rs485.yaml#
 
 properties:
   compatible: