New initramfs hook that uses LEDs etc. to let us know pmOS booted (when networking and screen don't work)

Created by: ollieparanoid

This idea was brought up the other day in #postmarketOS: An initramfs hook that tries to notify the user with alternative means that the kernel is actually booted:

let the LEDs blink
use the vibration motor
use the flashlight
...

When the device does not respond over USB, and the screen does not work either, this would be an easy way to verify that postmarketOS has booted on the device.

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