leds: Use modified led driver from enrc2b kernel

Driver contains cleanups and adds a button backlight brightness sysfs
interface.

Authors: Max Weniger and Xmister.

Commits:
  * BIG FAT warning cleanup
  * led: disabled currents for green and amber cause they do dont work correctly
  * led: added button brightness sysfs interface - thanks xmister
  * led: apply button brightness change only if on
  * led: derp - dont change backlight_mode
  * led: cleanup that log mess
  * led: another derp
  * led: limit BLN brightness to button brightness
  * led: remove HTC derp
  * leds: add custom option if slow blink brightness should be limited to button brightness - default is true
  * leds: fix currents interface

Change-Id: I47f4afa3f320abb32a9532b6c7880ea24605ae49