microchip-pickit2: first driver implementation (acquisition works, triggers don't)

microchip-pickit2: first driver implementation (acquisition works, triggers don't)

Fill in the scan, open/close, get/set/list, acquisition start/stop logic
such that data acquisition with a PICkit2 works.

Trigger support needs more attention. User specified triggers either
seem to not take effect, or the trigger position is not in the expected
location. It's yet to get determined what's the issue.

This implementation is based on protocol information gathered from the
pk2-la project.