staging: iio: light: Adding driver for ISL29018 ALS

adding support for the ISL 29018 ambient light and proximity sensor.

Addressed comments from reviews by Jonathan Cameron and Joe Perches
  * Removed some excess dbg prints that only printed function name
  * Renamed some properties to make them more descriptive
  * Added a property to list available adc resolutions
  * Defined arrays for resolutions/ranges as static const
  * Change loops initialization to memset for extensibility.
    * used sizeof() instead of ARRAY_SIZE() to be safer
  * Added a property to list available adc ranges
  * Fixed warnings and property names.

Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>