dt-bindings: net: ethernet-controller: add 2.5G and 10G speeds

Both are already used by HW and drivers inside Linux.

Fix warnings as:
arch/arm64/boot/dts/freescale/fsl-ls1028a-kontron-sl28-var2.dt.yaml: ethernet@0,2: fixed-link:speed:0:0: 2500 is not one of [10, 100, 1000]
        From schema: Documentation/devicetree/bindings/net/ethernet-controller.yaml

Signed-off-by: David Heidelberg <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Rob Herring <[email protected]>

Documentation/devicetree/bindings/net/ethernet-controller.yaml

@@ -178,7 +178,7 @@ properties:
                   Duplex configuration. 0 for half duplex or 1 for
                   full duplex
 
-              - enum: [10, 100, 1000]
+              - enum: [10, 100, 1000, 2500, 10000]
                 description:
                   Link speed in Mbits/sec.
 
@@ -200,7 +200,7 @@ properties:
               description:
                 Link speed.
               $ref: /schemas/types.yaml#/definitions/uint32
-              enum: [10, 100, 1000]
+              enum: [10, 100, 1000, 2500, 10000]
 
             full-duplex:
               $ref: /schemas/types.yaml#/definitions/flag