Added NRF52840 power management core functionality:
- Boot‑voltage lockout
- Initial support for shutdown/reset reason storage and capture (via RESETREAS/GPREGRET2)
- LPCOMP wake (for voltage-driven shutdowns)
- VBUS wake (for voltage-driven shutdowns)
- Per-board shutdown handler for board-specific tasks
- Exposed CLI queries for power‑management status in CommonCLI.cpp
- Added documentation in docs/nrf52_power_management.md.
- Enabled power management support in Xiao nRF52840, RAK4631, Heltec T114 boards
The Xiao nRF52840 combined with the Wio-SX1262 is often used for
cheap and compact DIY companion nodes. The Wio actually has an onboard
pushbutton that can be used as user button. Enable support for the
button.
Signed-off-by: Frieder Schrempf <frieder@fris.de>
