iio: driver for Semtech SX9500 proximity solution

Supports buffering, IIO events and changing sampling frequency.

Datasheet available at:
http://www.semtech.com/images/datasheet/sx9500_ag.pdf



Signed-off-by: Vlad Dogaru <vlad.dogaru@intel.com>
Reviewed-by: Hartmut Knaack <knaack.h@gmx.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>