dt-bindings: usb: Add binding for Realtek RTS5411 hub controller

The Realtek RTS5411 is a USB 3.0 hub controller with 4 ports.

This initial version of the binding only describes USB related
aspects of the RTS5411, it does not cover the option of
connecting the controller as an i2c slave.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Link: https://lore.kernel.org/r/20210609150159.v12.1.I248292623d3d0f6a4f0c5bc58478ca3c0062b49a@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>