dt-bindings: iio: accel: add dt-binding schema for msa311 accel driver

Introduce devicetree binding json-schema for MSA311 tri-axial,
low-g accelerometer driver.

Signed-off-by: Dmitry Rokosov <ddrokosov@sberdevices.ru>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220822175011.2886-5-ddrokosov@sberdevices.ru


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>