Draft: intel: implement support for RPC-powered xmm7360

Continue work on !1200 (closed) in a new clean merge request.

Open review comments from the original MR:

• Call the FCC unlock parts from a separate script in data/dispatcher-fcc-unlock/8086:7360, e.g. using a DBUS call (and mmcli) or by running the method mm_broadband_modem_xmm7360_check_fcc_lock in a separate tool written in C.
• If the code finds that the modem is FCC locked during power-up, it will fail with an error of type MM_CORE_ERROR_RETRY and the logic in mm-iface-modem.c will run the unlock script before retrying.
• Don't let mm_port_serial_xmmrpc_xmm7360_command (and xmm7360_command_to_byte_array) take ownership of the GByteArray body (and be responsible for freeing it), but make sure that the callers that pass that argument, also free it, e.g. using g_autoptr().
• @aleksm Please lock comments in this MR and add me as a developer so that we can discuss the changes being introduced by the MR.