dt-bindings: phy: Add Marvell COMPHY clocks

Marvell CP110 COMPHY block is fed by 3 clocks. Describe each of them in the
bindings.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

Documentation/devicetree/bindings/phy/phy-mvebu-comphy.txt

@@ -25,6 +25,13 @@ Required properties:
 - #address-cells: should be 1.
 - #size-cells: should be 0.
 
+Optional properlties:
+
+- clocks: pointers to the reference clocks for this device (CP110 only),
+          consequently: MG clock, MG Core clock, AXI clock.
+- clock-names: names of used clocks for CP110 only, must be :
+               "mg_clk", "mg_core_clk" and "axi_clk".
+
 A sub-node is required for each comphy lane provided by the comphy.
 
 Required properties (child nodes):
@@ -39,6 +46,9 @@ Examples:
 		compatible = "marvell,comphy-cp110";
 		reg = <0x120000 0x6000>;
 		marvell,system-controller = <&cpm_syscon0>;
+		clocks = <&CP110_LABEL(clk) 1 5>, <&CP110_LABEL(clk) 1 6>,
+			 <&CP110_LABEL(clk) 1 18>;
+		clock-names = "mg_clk", "mg_core_clk", "axi_clk";
 		#address-cells = <1>;
 		#size-cells = <0>;