make new API to retrieve group identifier level1

For mvno, user can add or edit mvno data field. To pre-provide
the mvno data of the edited apn when the user selects one of
the mvno types, need to support IMSI, SPN, and GID1 data.
To support GID1, make API to retrieve group identifier level1.

bug:6445254
Change-Id: I1bc280054cc7cd37e78a279866cefd62872a19fb
3 files changed