dt-bindings: net: cdns,macb: Add pic64gx compatibility

The pic64gx uses an identical integration of the macb IP to mpfs.

Signed-off-by: Pierre-Henry Moussay <[e-mail]>
Signed-off-by: Conor Dooley <[e-mail]>
Acked-by: Nicolas Ferre <[e-mail]>
Acked-by: Rob Herring (Arm) <[e-mail]>
Link: https://patch.msgid.link/20251117-easter-machine-37851f20aaf3@spud
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/devicetree/bindings/net/cdns,macb.yaml

···
               - cdns,sam9x60-macb     # Microchip sam9x60 SoC
               - microchip,mpfs-macb   # Microchip PolarFire SoC
           - const: cdns,macb          # Generic
-
+      - items:
+          - const: microchip,pic64gx-macb # Microchip PIC64GX SoC
+          - const: microchip,mpfs-macb    # Microchip PolarFire SoC
+          - const: cdns,macb              # Generic
       - items:
           - enum:
               - atmel,sama5d3-macb    # 10/100Mbit IP on Atmel sama5d3 SoCs