dt-bindings: mbox: add pic64gx mailbox compatibility to mpfs mailbox

pic64gx mailbox is compatible with mpfs mailbox, even if the mailbox
consumer is not - the underlying communication mechanism is the same.

Signed-off-by: Pierre-Henry Moussay <pierre-henry.moussay@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

Author: Pierre-Henry Moussay

Documentation/devicetree/bindings/mailbox/microchip,mpfs-mailbox.yaml

@@ -11,7 +11,11 @@ maintainers:
 
 properties:
   compatible:
-    const: microchip,mpfs-mailbox
+    oneOf:
+      - items:
+          - const: microchip,pic64gx-mailbox
+          - const: microchip,mpfs-mailbox
+      - const: microchip,mpfs-mailbox
 
   reg:
     oneOf: