USB: qcserial: Add support for Qualcomm Gobi 2000 devices

Add ids for Qualcomm Gobi 2000 QDL and Modem modes. Gobi 2000 has a
single altsetting in QDL mode, so adapt code to handle that.

Firmware upload protocol is also slightly different, with an
additional firmware file. However, qcserial doesn't handle firmware
uploading.

Tested on Lenovo Thinkpad T510.

Signed-off-by: Anssi Hannula <anssi.hannula@gmail.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>