dt-bindings: exynos: move ADC binding to iio/adc/ directory

Bindings are supposed to be organized by device class/function. Move the
binding for Exynos ADC to the iio/adc/ binding directory.

Signed-off-by: Rob Herring <robh@kernel.org>

diff --git a/Documentation/devicetree/bindings/arm/samsung/exynos-adc.txt b/Documentation/devicetree/bindings/iio/adc/samsung,exynos-adc.txt
similarity index 100%
rename from Documentation/devicetree/bindings/arm/samsung/exynos-adc.txt
rename to Documentation/devicetree/bindings/iio/adc/samsung,exynos-adc.txt