Bug : 62663757
If sys.display.low_persistence_mode_brightness is set, get brightness
from sys.display.low_persistence_mode_brightness.
Change-Id: I21a7583f535f8797300bab738cc4c8805ca06b90
Move it to vendor to work with generic AOSP system image.
Bug: 37927875
Test: The lib is under /vendor/lib(64)/hw instead of /system/lib(64)/hw
and the resulted system/vendor images work on the device.
Change-Id: I8218120bc870b64959f5a9929c5fdea703b7fb0c
The file /sys/class/leds/button-backlight/brightness isn't
created/exposed by the kernel.
Bug: 36097008
Test: LightHidlTest.TestSupported now passes.
Change-Id: If2e036cfa9fdb36596bc0820480072fde7591112