dt-bindings: usb: Add binding for Genesys Logic GL850G hub controller

The Genesys Logic GL850G is a USB 2.0 Single TT hub controller that
features 4 downstream ports, an internal 5V-to-3.3V LDO regulator (can
be bypassed) and an external reset pin.

Add a device tree binding for its USB protocol part. The internal LDO is
not covered by this and can just be modelled as a fixed regulator.

Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221206055228.306074-3-uwu@icenowy.me
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>