iio: adc: Allow selection of Exynos ADC on S5PV210

Make it possible to use Exynos ADC driver on S5PV210 based devices.

Signed-off-by: Jonathan Bakker <xc-racer2@live.ca>
Signed-off-by: Paweł Chmiel <pawel.mikolaj.chmiel@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>