dt-bindings: iio: Use unevaluatedProperties for SPI devices

dt-bindings: iio: Use unevaluatedProperties for SPI devices

SPI devices should use unevaluatedProperties:false instead of
additionalProperties:false, to allow any SPI device properties listed in
spi-peripheral-props.yaml.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://patch.msgid.link/20250324125313.82226-2-krzysztof.kozlowski@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>