iio: Add IIO_DELTA_VELOCITY channel type

iio: Add IIO_DELTA_VELOCITY channel type

The delta velocity is defined as a piece-wise integration of
acceleration data. The delta velocity represents the linear velocity
change between two consecutive measurements and it
is measured in m / s (meters per second).

In order to track the total linear velocity change during a desired
period of time, simply sum-up the delta velocity 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/20230808075059.645525-3-ramona.bolboaca@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>