dt-bindings: iio: dac: ad5791: Add optional reset, clr and ldac gpios

Depending on board layout, the ad57xx may need control of reset, clear,
and ldac pins by the host driver. Add optional bindings for these gpios.

Reviewed-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Axel Haslam <ahaslam@baylibre.com>
Link: https://patch.msgid.link/20241031071746.848694-2-ahaslam@baylibre.com


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