Ambient light sensor for Pegatron Lucid.  Supports pre-existing
ls_switch sysfs interface to en/disable automatic control, and exports
the brightness from the device as "ls_value".
Signed-off-by: NAndy Ross <andy.ross@windriver.com>
Signed-off-by: NCorentin Chary <corentin.chary@gmail.com>
Signed-off-by: NMatthew Garrett <mjg@redhat.com>