dt-binding: ARM: add clock binding docs for Marvell Berlin2 SoCs

This adds mandatory device tree binding documentation for the clock related
IP found on Marvell Berlin2 (BG2, BG2CD, and BG2Q) SoCs to the Berlin SoC
binding documentation.
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>

Documentation/devicetree/bindings/arm/marvell,berlin.txt

@@ -23,3 +23,50 @@ SoC and board used. Currently known SoC compatibles are:
 
 	...
 }
+
+* Marvell Berlin2 chip control binding
+
+Marvell Berlin SoCs have a chip control register set providing several
+individual registers dealing with pinmux, padmux, clock, reset, and secondary
+CPU boot address. Unfortunately, the individual registers are spread among the
+chip control registers, so there should be a single DT node only providing the
+different functions which are described below.
+
+Required properties:
+- compatible: shall be one of
+	"marvell,berlin2-chip-ctrl" for BG2
+	"marvell,berlin2cd-chip-ctrl" for BG2CD
+	"marvell,berlin2q-chip-ctrl" for BG2Q
+- reg: address and length of following register sets for
+  BG2/BG2CD: chip control register set
+  BG2Q: chip control register set and cpu pll registers
+
+* Clock provider binding
+
+As clock related registers are spread among the chip control registers, the
+chip control node also provides the clocks. Marvell Berlin2 (BG2, BG2CD, BG2Q)
+SoCs share the same IP for PLLs and clocks, with some minor differences in
+features and register layout.
+
+Required properties:
+- #clock-cells: shall be set to 1
+- clocks: clock specifiers referencing the core clock input clocks
+- clock-names: array of strings describing the input clock specifiers above.
+    Allowed clock-names for the reference clocks are
+      "refclk" for the SoCs osciallator input on all SoCs,
+    and SoC-specific input clocks for
+      BG2/BG2CD: "video_ext0" for the external video clock input
+
+Clocks provided by core clocks shall be referenced by a clock specifier
+indexing one of the provided clocks. Refer to dt-bindings/clock/berlin<soc>.h
+for the corresponding index mapping.
+
+Example:
+
+chip: chip-control@ea0000 {
+	compatible = "marvell,berlin2-chip-ctrl";
+	#clock-cells = <1>;
+	reg = <0xea0000 0x400>;
+	clocks = <&refclk>, <&externaldev 0>;
+	clock-names = "refclk", "video_ext0";
+};