dt-bindings: iio: adc: Add NXP IMX93 ADC

The IMX93 SoC has a new ADC IP, so add binding documentation
for NXP IMX93 ADC.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Link: https://lore.kernel.org/r/20230117135137.1735536-3-haibo.chen@nxp.com


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