dt-bindings: iio: dac: use spi-peripheral-props.yaml

Instead of listing directly properties typical for SPI peripherals,
reference the spi-peripheral-props.yaml schema. This allows using all
properties typical for SPI-connected devices, even these which device
bindings author did not tried yet.

Remove the spi-* properties which now come via spi-peripheral-props.yaml
schema, except for the cases when device schema adds some constraints
like maximum frequency.

While changing additionalProperties->unevaluatedProperties, put it in
typical place, just before example DTS.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220816124321.67817-5-krzysztof.kozlowski@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

dt-bindings: iio: dac: adi,ad8801: Add missing binding document.

This device was missing a binding document. Simple binding with the
ad8803 requiring two both low and high references whilst the 8801
only has a high reference.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Gwenhael Goavec-Merou <gwenhael.goavec-merou@trabucayre.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20210627163244.1090296-15-jic23@kernel.org