nvethernet: Document mdc-cr DT property

This patch adds Device Tree binding documentation for the mdc-cr
property used in the nvethernet driver.

This property configures the MDC clock rate for the MDIO interface.

Bug 5147775

Change-Id: Iad49e9e41741f975a6dc329cce1308dc4af87ba5
Signed-off-by: Bhadram Varka <vbhadram@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nv-oot/+/3339678
Reviewed-by: svcacv <svcacv@nvidia.com>
Reviewed-by: Srinivas Ramachandran <srinivasra@nvidia.com>
GVS: buildbot_gerritrpt <buildbot_gerritrpt@nvidia.com>

Documentation/devicetree/bindings/net/ethernet/nvidia/nvethernet/nvidia,tegra264-mgbe.yaml

@@ -579,6 +579,11 @@ properties:
         minimum: 0x8
         maximum: 0x8
 
+    nvidia,mdc-cr:
+        $ref: "/schemas/types.yaml#/definitions/uint32"
+        minimum: 0x0
+        maximum: 0xF
+
 required:
     - compatible
     - reg