nexus-osciprime: basic scanning functionality

nexus-osciprime: basic scanning functionality

Unfortunately the device doesn't have an EEPROM on board at all, and so
initially enumerates with the default Cypress FX2 VID:PID (04b4:8613).
Since we already support using plain FX2* as basic logic analyzers using
the fx2lafw firmware, we cannot support that same VID:PID for the
OsciPrime. Therefore a USB conn is required for the initial scan.

However, once the firmware is uploaded the device re-enumerates as
04b4:1004, which we do detect for scanning automatically.

Thus, the OsciPrime driver requires one scan with conn parameter to get
the firmware uploaded, but it will then keep working until powered off.