init: turn off backlight when performing shutdown cleanup

(cherry pick from commit a98cc9c2)

Try writing a "0" into:

- /sys/class/leds/lcd-backlight/brightness
- /sys/class/backlight/*/brightness

to turn off the backlight during shutdown cleanup.

Bug: 27506425
Change-Id: Ic8a44dc8909b303f24e14f71cfb43292df60efde