dt-bindings: net: snps,dwmac: add new property snps,clk-csr

Add description for new property snps,clk-csr in binding file
Signed-off-by: Jianguo Zhang <jianguo.zhang@mediatek.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/snps,dwmac.yaml

@@ -289,6 +289,11 @@ properties:
       is supported. For example, this is used in case of SGMII and
       MAC2MAC connection.
 
+  snps,clk-csr:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      Frequency division factor for MDC clock.
+
   mdio:
     $ref: mdio.yaml#
     unevaluatedProperties: false