dt-bindings: usb: usb251xb: Convert to YAML schema

Convert the usb251xb hub DT bindings from text to yaml schema so it is
possible to validate DTs against the schema.

Adjust the example to describe two different hubs at different I2C bus
addresses, to avoid I2C address collission in the example.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20221107134248.21899-1-marex@denx.de


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