quectel: add support for RM520N

RM520N in USB mode exposes the following: ttyUSB0 (if #0): QCDM/DIAG port ttyUSB1 (if #1 (closed)): GPS data port ttyUSB2 (if #2 (closed)): AT primary port ttyUSB3 (if #3 (closed)): AT secondary port

So, lets mark them so ModemManager can properly manage them.

Signed-off-by: Robert Marko robert.marko@sartura.hr