Staging: IIO: lis3l02dq ring buffer and data ready trigger support

Example of relatively common case of device sampling
based on internal clock and providing a data ready
signal to indicate that new data is available to be
read out.

Generic trigger approach used to allow other devices
to be sampled 'at the same time' as this the accelerometer.
This is very useful in various motion estimation algorithms.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>