Odroid-X, -X2, -XU3 and -XU4 have SOC-ADC routed to an external connector.
Enable the ADC for use as iio-device.
Signed-off-by: Markus Reichl <m.reichl@fivetechno.de>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>