staging: iio: adis16260 add suppport for adis16255 and adis16250.

Unusual element is addition of 'negate' and 'axis' platform data
to ensure we support all the functionality of the adis16255 driver
currently in staging.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Acked-by: Matthias Brugger <mensch0815@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>