usb: usb251xb: Add US port lanes inversion property

The driver bindings already declare the "swap-dx-lanes" property to
invert the downstream ports lanes polarity. The similar config
can be defined for a single upstream port - "swap-us-lanes". It's
going to be boolean since there is only one upstream port
on the hub.

Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Acked-by: Richard Leitner <richard.leitner@skidata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>