USB: serial: option: add u-blox LARA-L6 modem

Add LARA-L6 PIDs for three different USB compositions.

LARA-L6 module can be configured (by AT interface) in three different
USB modes:
* Default mode (Vendor ID: 0x1546 Product ID: 0x1341) with 4 serial
interfaces
* RmNet mode (Vendor ID: 0x1546 Product ID: 0x1342) with 4 serial
interfaces and 1 RmNet virtual network interface
* CDC-ECM mode (Vendor ID: 0x1546 Product ID: 0x1343) with 4 serial
interface and 1 CDC-ECM virtual network interface

In default mode LARA-L6 exposes the following interfaces:
If 0: Diagnostic
If 1: AT parser
If 2: AT parser
If 3: AT parser/alternative functions

In RmNet mode LARA-L6 exposes the following interfaces:
If 0: Diagnostic
If 1: AT parser
If 2: AT parser
If 3: AT parset/alternative functions
If 4: RMNET interface

In CDC-ECM mode LARA-L6 exposes the following interfaces:
If 0: Diagnostic
If 1: AT parser
If 2: AT parser
If 3: AT parset/alternative functions
If 4: CDC-ECM interface

Signed-off-by: Davide Tronchin <davide.tronchin.94@gmail.com>
[ johan: drop PID defines in favour of comments ]
Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>