dt-bindings: serial: fsl-lpuart: allow other serial properties

Reference common serial properties bindings to allow typical serial
properties:

  imx8qxp-ai_ml.dtb: serial@5a060000: Unevaluated properties are not allowed ('uart-has-rtscts' were unexpected)

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230124091916.45054-7-krzysztof.kozlowski@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>