dt-bindings: iio: adc: ep93xx: Add cirrus,ep9301-adc description

Add device tree bindings for Cirrus Logic EP9301/EP9302 internal SoCs' ADC
block.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Link: https://lore.kernel.org/r/20221223162636.6488-1-alexander.sverdlin@gmail.com


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