devicetree: bindings: Document qcom,gcc

Document the global clock controller found on Qualcomm devices.

Cc: <devicetree@vger.kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

Documentation/devicetree/bindings/clock/qcom,gcc.txt

+Qualcomm Global Clock & Reset Controller Binding
+------------------------------------------------
+
+Required properties :
+- compatible : shall contain only one of the following:
+
+			"qcom,gcc-msm8660"
+			"qcom,gcc-msm8960"
+			"qcom,gcc-msm8974"
+
+- reg : shall contain base register location and length
+- #clock-cells : shall contain 1
+- #reset-cells : shall contain 1
+
+Example:
+	clock-controller@900000 {
+		compatible = "qcom,gcc-msm8960";
+		reg = <0x900000 0x4000>;
+		#clock-cells = <1>;
+		#reset-cells = <1>;
+	};