dt-bindings: adc: axi-adc: update bindings for backend framework

'adi,adc-dev' is now deprecated and must not be used anymore. Hence,
also remove it from being required.

The reason why it's being deprecated is because the axi-adc CORE is now
an IIO service provider hardware (IIO backends) for consumers to make use
of. Before, the logic with 'adi,adc-dev' was the opposite (it was kind
of consumer referencing other nodes/devices) and that proved to be wrong
and to not scale.

Now, IIO consumers of this hardware are expected to reference it using the
io-backends property. Hence, the new '#io-backend-cells' is being added
so the device is easily identified as a provider.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240210-iio-backend-v11-2-f5242a5fb42a@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

dt-bindings: iio: cleanup examples - indentation

Use 4-space indentation (for cases when it is neither 4 not 2 space).

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Alexandru Lazar <alazar@startmail.com> # max1241
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230124081037.31013-5-krzysztof.kozlowski@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

dt-bindings: iio: adc: axi-adc: update maintainers

Update bindings maintainerns section.

Signed-off-by: Alexandru Tachici <alexandru.tachici@analog.com>
Acked-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20220526134603.75216-4-alexandru.tachici@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

dt-bindings: iio: adc: add bindings doc for AXI ADC driver

This change adds the bindings documentation for the AXI ADC driver.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>