staging:iio:gyro: adis16080 cleanup, move to abi and bug fixes.

Moved to standard sysfs naming and got rid of direct register writing
from userspace.

The rx and tx buffers are never used together so just have one and
avoid the need to malloc it by using putting it in the state structure
and using the ____cacheline_aligned trick.

Couple of obvious bug fixes whilst I was here.

I don't have one of these so can't test. This is done off datasheet.
Note that as with the adis16060 driver there are parts that definitely
wouldn't work before this patch.  Now it 'might' assuming I haven't
messed up too badly.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>