dt-bindings: serial: cdsn,uart: add power-domains

Few Xilinx DTS have power domains in serial node:

  zynqmp-zc1232-revA.dtb: serial@ff000000: Unevaluated properties are not allowed ('power-domains' was unexpected)

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Michal Simek <michal.simek@amd.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230124091916.45054-3-krzysztof.kozlowski@linaro.org


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