Reset via NVIC_SystemReset() not working with MCUBoot enabled on nRF5340 custom board

[responsible_duck]

I posted my configuration in a separate discussion. 

Calling this method works when CONFIG_BOOTLOADER_MCUBOOT=n works. But as soon as we flash an image with MCUBoot enabled, calling `NVIC_SystemReset()` doesn't do a full reset it simply powers off. We have to power cycle to truly reset the device.

Extraneous info but the issue is that we need to enter serial recovery mode but we do not have a physical way to power cycle without the battery dying so we need a way to reset the device in the firmware. 

[responsible_duck]

Hardware reset line low doesn't work either and only a power cycle works :/