liblights: Fix & improve notification light

Use the new touchkey_enabled control to disable or enable the
illumination of the key leds when one of the key led buttons is pressed.
Thus fixing the notification light as the previously used onoff
disables the key leds completely.

Change the notification light logic:
The color is no longer interpreted as a field to control each led seperately.
Instead the brightness values for white and blue are calculated for all leds
at once in a way to utilize both, the white and the blue led.

Change the handling for special modes:
The special mode is determined by the lower 4 bits of the colors values.
Its speed is selected by the pulse length (i.e. flashOn).
It is activated if the pulse speed is set to custom (i.e. flashOff=0).
This can be achieved by first setting the pulse length to "always on"
and after that choosing another pulse length.

Fix some compiler warnings and do some cleanup.

Change-Id: I0730324217479aee16be8647a6805b42e6d21378
liblights: Enable key led brightness control

Set the key led brightness to the same value as the lcd brightness.

Change-Id: I988ead747d5cf2a07c96368c895a9261538afeeb
BoardConfig.mk: Enable auto-brightness for key leds

BOARD_SYSFS_LIGHT_SENSOR now contains two filenames,
one for the lcd-display and one for the key leds.

Change-Id: I813a712308e31d7e2c291e8171f25015d032e030