RM6785: lights: Fix brightness curve

* These devices report values in 0-2047 or 0-4095 which results in
  extremely uneven behaviour in brightness slider
* Map brightness values logarithmatically to match aosp behaviour
* Generated using https://gist.github.com/SamarV-121/3fe97552db73d9cc673ce7cf250d27b7

Change-Id: I794fdca04bb29b8431fd20b769fc09749481645b
2 files changed