Settings: make CM's adjust auto brightness configurable (2/2)

added  config_automatic_adjust_brightness_available to
config.xml to give the abillity to turn this feature off.
Reason is that some devices which are using own light sensor
systems (like some sony and htc) cannot be controlled
over that because some sensors are reporting back
wrong values.

Default value: true

but is depending on the config_automatic_brightness_available
value.

cheers

Change-Id: I0655712df25a9291e48c824657503b0cead83609