iio: adc: add exynos adc driver under iio framwork

This patch adds New driver to support:
1. Supports ADC IF found on EXYNOS4412/EXYNOS5250
   and future SoCs from Samsung
2. Add ADC driver under iio/adc framework
3. Also adds the Documentation for device tree bindings

Signed-off-by: Naveen Krishna Chatradhi <ch.naveen@samsung.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 00213ea..a40d3c2 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -103,6 +103,13 @@
 	help
 	  Say yes here to build support for Atmel AT91 ADC.
 
+config EXYNOS_ADC
+	bool "Exynos ADC driver support"
+	help
+	  Core support for the ADC block found in the Samsung EXYNOS series
+	  of SoCs for drivers such as the touchscreen and hwmon to use to share
+	  this resource.
+
 config LP8788_ADC
 	bool "LP8788 ADC driver"
 	depends on MFD_LP8788