Now that the adis library no longer depends on the sw_ring buffer implementation
we can move it out of staging.

While we are at it also sort the entries in the iio Kconfig and Makefile to be
in alphabetical order.
Signed-off-by: NLars-Peter Clausen <lars@metafoo.de>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

A lot of the devices from the ADIS family use the same methods for accessing
registers, sampling data and trigger handling. They also have similar register
layout for the control registers.

This patch adds a common library for these devices. The library implements
functions for reading and writing registers as buffer and trigger management. It
also provides a set functions for accessing the control registers and for
running the devices internal self-test. Having this common library code will
allow us to remove a lot of duplicated code.
Signed-off-by: NLars-Peter Clausen <lars@metafoo.de>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>