scripts: runners: nrf: Default to soft reset for the nRF52 series

[carlescufi]

scripts: runners: nrf: Default to soft reset for the nRF52 series

The Nordic nRF52 series have a peculiarity that is not shared with any
other Nordic families of SoCs: the reset pin can be reconfigured as a
regular GPIO. This has an unintended consequence: if the user has
reconfigured the pin in Devicetree to be a GPIO, `west flash` will
override that and configure the IC to use it as a reset pin, and the firmware
at boot won't be able to switch it back to GPIO, because that requires a UICR
erase. This behavior is very confusing to users, because the GPIO does
not work at all, since it is now just a reset line.

With this patch, `west flash` defaults to using soft reset instead of
pin reset for the nRF52 family of devices, to avoid overwriting the
reset pin configuration that the user includes in the image.

In order to be able to continue to use pin reset for users that so
desire it, a new option `--pinreset` is added that forces the use of pin
reset. The existing `--softreset` option is left exactly as it was, but
it is now applicable only to families other than the nRF52.

[fabiobaltieri]

Looks good fell for this few times myself as well, flashing a custom board with a hacked nrf52dk image and then go to the custom firmware and the pin is still mysteriously not working until one does a uicr reset, I presume that the counter-case of this would be if the board has something else connected to that reset line in addition to the nrf chip? Anyway looks good. (just checked the last patch)

[carlescufi]

Thanks @fabiobaltieri!

Looks good fell for this few times myself as well, flashing a custom board with a hacked nrf52dk image and then go to the custom firmware and the pin is still mysteriously not working until one does a uicr reset,

Glad to hear that this will be useful for you too, it's a common issue.

I presume that the counter-case of this would be if the board has something else connected to that reset line in addition to the nrf chip?

Not sure I get that. This solves the problem of having something (e.g. MISO line for an SPI link) connected to the nRESET pin and west flash making that unavailable because it has configured it as nRESET instead of GPIO. The counter case would be using it as reset?

Last push is just for a couple of test updates.

[carlescufi]

Last push: rebase