iio: Add IIO_DELTA_ANGL channel type

iio: Add IIO_DELTA_ANGL channel type

The delta angle is defined as a piece-wise integration of angular
velocity data. The delta angle represents the amount of
angular displacement between two consecutive measurements and it
is measured in radians.

In order to track the total angular displacement during a desired
period of time, simply sum-up the delta angle samples acquired
during that time.

IIO currently does not offer a suitable channel type for this
type of measurements hence this patch adds it.

Signed-off-by: Ramona Bolboaca <ramona.bolboaca@analog.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20230808075059.645525-2-ramona.bolboaca@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>