dt-bindings: iio: light: add support for Dyna-Image AL3320A

This commit add dt-bindings support to al3320a driver and vendor-prefix
dynaimage.
Partly based on unmerged commit:
"iio: Add Dyna-Image AP3223 ambient light and proximity driver"

Signed-off-by: David Heidelberg <david@ixit.cz>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>