dt-bindings: net: mscc-miim: add microchip,lan9691-miim

Document Microchip LAN969x MIIM compatible.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20251229184004.571837-11-robert.marko@sartura.hr
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/mscc,miim.yaml

@@ -14,9 +14,14 @@ allOf:
 
 properties:
   compatible:
-    enum:
-      - mscc,ocelot-miim
-      - microchip,lan966x-miim
+    oneOf:
+      - enum:
+          - mscc,ocelot-miim
+          - microchip,lan966x-miim
+      - items:
+          - enum:
+              - microchip,lan9691-miim
+          - const: mscc,ocelot-miim
 
   "#address-cells":
     const: 1