samples: sensor: adxl372: Add ADXL372 sample application

This sample application produces slightly different outputs based on
the chosen driver configuration mode. In Measuring Mode with trigger
support, the acceleration on all three axis is printed in m/s^2 at
the sampling rate (ODR). In polled Measuring Mode the instantaneous
acceleration is polled every 2 seconds. In most high-g applications,
a single (3-axis) acceleration sample at the peak of an impact event
contains sufficient information about the event, and the full
acceleration history is not required.
In this Max Peak Detect Mode the device returns only the over
threshold peak acceleration between two consecutive sample fetches or
trigger events. Instead of printing the acceleration on all three axis,
the sample application calculates the vector magnitude
(root sum squared) and displays the result in g rather than in m/s^2,
together with an bar graph.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>