Add support for Nordic's new nRF Util tool, aka nrfutil. Via its
"device" command, nrfutil now supports most of the functionality offered
by nrfjprog.
The tool itself can be found here:
https://www.nordicsemi.com/Products/Development-tools/nrf-util
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>
