dt-bindings: usb: ci-hdrc-usb2: Allow "fsl,imx27-usb" to be passed alone

dt-bindings: usb: ci-hdrc-usb2: Allow "fsl,imx27-usb" to be passed alone

imx27.dtsi describes its usb nodes as:

compatible = "fsl,imx27-usb";

Adjust the bindings to allow it and avoid the following schema warning:

usb@10024000: compatible: 'oneOf' conditional failed, one must be fixed:
	['fsl,imx27-usb'] is too short

Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230924160351.692867-1-festevam@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>