net: qmi_wwan: support Sierra Wireless MC77xx devices in QMI mode

The MC77xx devices can operate in two modes: "Direct IP" or "QMI",
switchable using a password protected AT command.  Both product ID
and USB interface configuration will change when switched.

The "sierra_net" driver supports the "Direct IP" mode.  This driver
supports the "QMI" mode.

There are also multiple possible USB interface configurations in each
mode, some providing more than one wwan interface.  Like many other
devices made for Windows, different interface types are identified
using a static interface number.  We define a Sierra specific
interface whitelist to support this.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>