Documentation: DT: Add iproc-static-adc binding

The patch adds devicetree binding document for broadcom's
iproc-static-adc controller driver.
Signed-off-by: Raveendra Padasalagi <raveendra.padasalagi@broadcom.com>
Reviewed-by: Ray Jui <ray.jui@broadcom.com>
Reviewed-by: Scott Branden <scott.branden@broadcom.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/brcm,iproc-static-adc.txt

+* Broadcom's IPROC Static ADC controller
+
+Broadcom iProc ADC controller has 8 channels 10bit ADC.
+Allows user to convert analog input voltage values to digital.
+
+Required properties:
+
+- compatible: Must be "brcm,iproc-static-adc"
+
+- adc-syscon: Handler of syscon node defining physical base address of the
+  controller and length of memory mapped region.
+
+- #io-channel-cells = <1>; As ADC has multiple outputs
+  refer to Documentation/devicetree/bindings/iio/iio-bindings.txt for details.
+
+- io-channel-ranges:
+  refer to Documentation/devicetree/bindings/iio/iio-bindings.txt for details.
+
+- clocks: Clock used for this block.
+
+- clock-names: Clock name should be given as tsc_clk.
+
+- interrupts: interrupt line number.
+
+For example:
+
+	ts_adc_syscon: ts_adc_syscon@180a6000 {
+		compatible = "brcm,iproc-ts-adc-syscon","syscon";
+		reg = <0x180a6000 0xc30>;
+	};
+
+	adc: adc@180a6000 {
+		compatible = "brcm,iproc-static-adc";
+		adc-syscon = <&ts_adc_syscon>;
+		#io-channel-cells = <1>;
+		io-channel-ranges;
+		clocks = <&asiu_clks BCM_CYGNUS_ASIU_ADC_CLK>;
+		clock-names = "tsc_clk";
+		interrupts = <GIC_SPI 164 IRQ_TYPE_LEVEL_HIGH>;
+		status = "disabled";
+	};