west: nrfjprog: Allow flashing UICR without erase

Currently, it is not possible to use a normal flash command to flash two
hex files that contain data in the UICR region, even though these
data don't conflict with each other.
However, that is not a technical limitation of the device, but of the
nrfjprog runner as it fails as soon as the hex file contained UICR data
and there was no --force/--erase/--recover used.
That approach was used in the past as program operation was used
without --verify, but as this option was added a while ago it is an
unnecessary limitation.

If the UICR wasn't erased before programming, the verify of the program
operation will now fail, so giving the user a warning in this case that
the hex files contain data in the UICR will still give the user a hint
of what might have caused the failing verify.
Additionally, it enables partial programming of the UICR without the
use of the --force option.

Signed-off-by: Markus Swarowsky <markus.swarowsky@nordicsemi.no>