broadband-modem-qmi: implement UE mode get/set
Instead of relying on getting/setting the UE mode via AT +CEMODE command which on Quectel RM520N (And I assume other QMI based modems) only allows getting the value and not setting one it has special AT commands for CS/PS and voice/data centric values.
So lets instead use the QMI Get/Set System Selection Preference TLV which offers service domain and usage domain preference info so we can use those to get/set the 3GPP TS 24.301 UE mode values.
Signed-off-by: Robert Marko robert.marko@sartura.hr
