USB: serial: option: add two-endpoints device-id flag

commit 35aecc02b5b621782111f64cbb032c7f6a90bb32 upstream

Allow matching on interfaces having two endpoints by adding a new
device-id flag.

This allows for the handling of devices whose interface numbers can
change (e.g. Quectel EP06) to be contained in the device-id table.

The upstream commit removes a variable that is still in use in the 4.14
version of the option-driver, so the removal is undone.

Tested-by: Kristian Evensen <kristian.evensen@gmail.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Kristian Evensen <kristian.evensen@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>