dt-bindings: iio: dac: ti,dac5571: Add DAC081C081 support

The DAC081C081 is a TI DAC whose software interface is compatible with
the DAC5571. It is the 8-bit version of the DAC121C081, already
supported by the DAC5571 bindings. Extends the bindings to support this
chip.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sean Nyekjaer <sean@geanix.com>
Link: https://lore.kernel.org/r/20240325203245.31660-2-laurent.pinchart@ideasonboard.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

dt-bindings: iio: use lowercase hex in examples

Use lowercase hex in addresses in examples.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230124081037.31013-4-krzysztof.kozlowski@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

dt-bindings: iio: ti-dac5571: Add ti,dac121c081

It works much the same as ti,dac7571, so it fits in the "family" even
if the name is a little bit different.

Reviewed-by: Sean Nyekjaer <sean@geanix.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Peter Rosin <peda@axentia.se>
Link: https://lore.kernel.org/r/a230b7a8-4146-9483-48ee-0bebdd945731@axentia.se
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

dt-bindings:iio:dac:ti,dac5571 yaml conversion.

A few tweaks in this conversion.
* The example didn't have the I2C address of 4C in the node name so
fixed that.
* The reference voltage in the txt file is an optional binding, but
the driver is making use of it to provide the scaling of the output
channels. As such I have made it required going forwards.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Sean Nyekjaer <sean@geanix.com>
Link: https://lore.kernel.org/r/20201031134110.724233-13-jic23@kernel.org