iio: devicetree: Add DT binding documentation for Exynos3250 ADC

This patch add DT binding documentation for Exynos3250 ADC IP. Exynos3250 has
special clock ('sclk_adc') for ADC which provide clock to internal ADC.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Naveen Krishna Chatradhi <ch.naveen@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/arm/samsung/exynos-adc.txt

@@ -14,14 +14,21 @@ Required properties:
 				for exynos4412/5250 controllers.
 			Must be "samsung,exynos-adc-v2" for
 				future controllers.
+			Must be "samsung,exynos3250-adc" for
+				controllers compatible with ADC of Exynos3250.
 - reg:			Contains ADC register address range (base address and
 			length) and the address of the phy enable register.
 - interrupts: 		Contains the interrupt information for the timer. The
 			format is being dependent on which interrupt controller
 			the Samsung device uses.
 - #io-channel-cells = <1>; As ADC has multiple outputs
-- clocks		From common clock binding: handle to adc clock.
-- clock-names		From common clock binding: Shall be "adc".
+- clocks		From common clock bindings: handles to clocks specified
+			in "clock-names" property, in the same order.
+- clock-names		From common clock bindings: list of clock input names
+			used by ADC block:
+			- "adc" : ADC bus clock
+			- "sclk" : ADC special clock (only for Exynos3250 and
+				   compatible ADC block)
 - vdd-supply		VDD input supply.
 
 Note: child nodes can be added for auto probing from device tree.
@@ -41,6 +48,20 @@ adc: adc@12D10000 {
 	vdd-supply = <&buck5_reg>;
 };
 
+Example: adding device info in dtsi file for Exynos3250 with additional sclk
+
+adc: adc@126C0000 {
+	compatible = "samsung,exynos3250-adc", "samsung,exynos-adc-v2;
+	reg = <0x126C0000 0x100>, <0x10020718 0x4>;
+	interrupts = <0 137 0>;
+	#io-channel-cells = <1>;
+	io-channel-ranges;
+
+	clocks = <&cmu CLK_TSADC>, <&cmu CLK_SCLK_TSADC>;
+	clock-names = "adc", "sclk";
+
+	vdd-supply = <&buck5_reg>;
+};
 
 Example: Adding child nodes in dts file