iio: adc: ad7124: add clock output support

iio: adc: ad7124: add clock output support

Add support for the AD7124's internal clock output. If the #clock-cells
property is present, turn on the internal clock output during probe.

If both the clocks and #clock-names properties are present (not allowed
by devicetree bindings), assume that an external clock is being used so
that we don't accidentally have two outputs fighting each other.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250828-iio-adc-ad7124-proper-clock-support-v3-4-0b317b4605e5@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>