usb: usb251xb: Add USB2517i specific struct and IDs

There are USB2517 and USB2517i hubs, which have almost the same
registers space as already supported USB251xBi series. The difference
it in DIDs and in a few functions. This patch adds the USB2517/i data
structures to the driver, so it would have different setting depending
on the device discovered on i2c-bus.

Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>