Enable backlight trigger for LCD

Disable backlight when blanked out.

(adapted from https://github.com/LineageOS/android_device_fairphone_FP2/commit/5e17a2f)
[move to 'on init' to make sure sepolicy for sysfs node has been set,
add sepolicy]

Ref: CRACKLING-626
Issue: FP2P-268
Change-Id: Ifc698c1470b086b0e1f083c3c234f272988d108c
(cherry picked from commit 3194d34793e814625d4dda4cea6279770ed415a3)
3 files changed