staging: iio: new adis16203 driver

IIO driver for Programmable 360 Degrees Inclinometer adis16203 parts.

Signed-off-by: Barry Song <barry.song@analog.com>
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>