Indicate when "lockdown mode" is triggered on the Librem 5
The Librem 5 hardware implements "lockdown mode" when all three hardware kill switches are engaged. Lockdown mode disables additional sensors on the Librem 5 hardware and is explained in depth here:
https://puri.sm/posts/lockdown-mode-on-the-librem-5-beyond-hardware-kill-switches/
We would like the ability to trigger other events in software when the Librem 5 is in this state, starting with an icon in Phosh (https://gitlab.gnome.org/World/Phosh/phosh/-/issues/559#note_1495086) and eventually allow the user to trigger other software-side changes (possibly lock the screen, unmount the SD card, or other security measures).
The first step in this would be for the kernel to detect and indicate in some way (dev or sys interface perhaps?) the current "lockdown mode" state.