Correct check box visibility in Display / Brightness

The check box for "Automatic brightness" should not be visible in
Brightness screen if the product configuration
config_automatic_brightness_available in config.xml is set to false.

Change-Id: I0d81137723d0eacd97aa88bf08b69e12dd4d73fa
Signed-off-by: Benn Porscke <benn.porscke@stericsson.com>