dt-bindings: net: dwmac-meson: Document the "timing-adjustment" clock

The PRG_ETHERNET registers can add an RX delay in RGMII mode. This
requires an internal re-timing circuit whose input clock is called
"timing adjustment clock". Document this clock input so the clock can be
enabled as needed.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/amlogic,meson-dwmac.yaml

@@ -40,18 +40,22 @@ allOf:
     then:
       properties:
         clocks:
+          minItems: 3
+          maxItems: 4
           items:
             - description: GMAC main clock
             - description: First parent clock of the internal mux
             - description: Second parent clock of the internal mux
+            - description: The clock which drives the timing adjustment logic
 
         clock-names:
           minItems: 3
-          maxItems: 3
+          maxItems: 4
           items:
             - const: stmmaceth
             - const: clkin0
             - const: clkin1
+            - const: timing-adjustment
 
         amlogic,tx-delay-ns:
           $ref: /schemas/types.yaml#definitions/uint32
@@ -120,7 +124,7 @@ examples:
          reg = <0xc9410000 0x10000>, <0xc8834540 0x8>;
          interrupts = <8>;
          interrupt-names = "macirq";
-         clocks = <&clk_eth>, <&clkc_fclk_div2>, <&clk_mpll2>;
-         clock-names = "stmmaceth", "clkin0", "clkin1";
+         clocks = <&clk_eth>, <&clk_fclk_div2>, <&clk_mpll2>, <&clk_fclk_div2>;
+         clock-names = "stmmaceth", "clkin0", "clkin1", "timing-adjustment";
          phy-mode = "rgmii";
     };