net: qmi_wwan: use a single bind function for all device types

Refactoring the bind code lets us use a common driver_info struct
for all supported devices, simplifying the code a bit.  The
real advantage is that devices using the CDC ECM interface
layout now also can be added dynamically using the new_id sysfs
interface.  This simplifies testing of new devices.

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