dt-bindings: ap806: add the cluster clock node in the syscon file

Document the device tree binding for the cluster clock controllers found
in the Armada 7K/8K SoCs.

Signed-off-by: Gregory CLEMENT <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Stephen Boyd <[e-mail]>

Documentation/devicetree/bindings/arm/marvell/ap806-system-controller.txt

···
 The Device Tree node representing the AP806 system controller provides
 a number of clocks:
 
- - 0: clock of CPU cluster 0
- - 1: clock of CPU cluster 1
+ - 0: reference clock of CPU cluster 0
+ - 1: reference clock of CPU cluster 1
  - 2: fixed PLL at 1200 Mhz
  - 3: MSS clock, derived from the fixed PLL
 
···
 		interrupt-parent = <&sei>;
 		interrupts = <18>;
 		#thermal-sensor-cells = <1>;
+	};
+};
+
+Cluster clocks:
+---------------
+
+Device Tree Clock bindings for cluster clock of AP806 Marvell. Each
+cluster contain up to 2 CPUs running at the same frequency.
+
+Required properties:
+- compatible: must be  "marvell,ap806-cpu-clock";
+- #clock-cells : should be set to 1.
+
+- clocks : shall be the input parent clock(s) phandle for the clock
+           (one per cluster)
+
+- reg: register range associated with the cluster clocks
+
+ap_syscon1: system-controller@6f8000 {
+	compatible = "marvell,armada-ap806-syscon1", "syscon", "simple-mfd";
+	reg = <0x6f8000 0x1000>;
+
+	cpu_clk: clock-cpu@278 {
+		compatible = "marvell,ap806-cpu-clock";
+		clocks = <&ap_clk 0>, <&ap_clk 1>;
+		#clock-cells = <1>;
+		reg = <0x278 0xa30>;
 	};
 };