dt-bindings: usb: rt1711h device tree binding document

Add device tree binding document for Richtek RT1711H Type-C chip driver

Signed-off-by: ShuFan Lee <shufan_lee@richtek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>