dt-bindings: iio: adi,ad7923: add adi,range-double property

Document the new property to enable doubling the analog input range.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220912081223.173584-4-nuno.sa@analog.com


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