usb: usb251xb: Add 5,6,7 ports mapping def setting

usb: usb251xb: Add 5,6,7 ports mapping def setting

USB2517 got three additionl downstream ports, which can
as well be mapped to another logical ports. USB251xb driver
currently doesn't fully support such setting configuration
from dts file. This patch doesn't change this, but adds
usb2517 spcific ports default liner mapping.

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>