iio: dac: ad3552r: add support for ad3541r and ad3551r

Add support for single-output DAC variants.

Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240522150141.1776196-5-adureghello@baylibre.org


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