Documentation: bindings: add reset bindings docs for Marvell Berlin SoCs

Add the reset binding documentation to the SoC binding documentation as
the reset driver in Marvell Berlin SoC is part of the chip/system
control registers. This patch adds the required properties to configure
the reset controller.
Signed-off-by: NAntoine Ténart <antoine.tenart@free-electrons.com>
Acked-by: NPhilipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: NSebastian Hesselbarth <sebastian.hesselbarth@gmail.com>

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

@@ -106,11 +106,21 @@ Required subnode-properties:
 - groups: a list of strings describing the group names.
 - function: a string describing the function used to mux the groups.
 
+* Reset controller binding
+
+A reset controller is part of the chip control registers set. The chip control
+node also provides the reset. The register set is not at the same offset between
+Berlin SoCs.
+
+Required property:
+- #reset-cells: must be set to 2
+
 Example:
 
 chip: chip-control@ea0000 {
 	compatible = "marvell,berlin2-chip-ctrl";
 	#clock-cells = <1>;
+	#reset-cells = <2>;
 	reg = <0xea0000 0x400>;
 	clocks = <&refclk>, <&externaldev 0>;
 	clock-names = "refclk", "video_ext0";