scripts: runners: nrf: Use nrfutil error codes

Standardize to nrfutil error codes instead of nrfjprog ones. This is
because nrfutil has a wider range of functionality and will eventually
be the default runner for all nRF devices. It is also consistent with
the internal operation representation, which is now using the nrfutil
format already.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>