dt-bindings: soc: microchip: add compatible for the mss-top-sysreg on pic64gx

pic64gx has an identical sysreg syscon to mpfs, add it using a fallback.

Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

Author: ConchuOD

Documentation/devicetree/bindings/soc/microchip/microchip,mpfs-mss-top-sysreg.yaml

@@ -15,10 +15,16 @@ description:
 
 properties:
   compatible:
-    items:
-      - const: microchip,mpfs-mss-top-sysreg
-      - const: syscon
-      - const: simple-mfd
+    oneOf:
+      - items:
+          - const: microchip,mpfs-mss-top-sysreg
+          - const: syscon
+          - const: simple-mfd
+      - items:
+          - const: microchip,pic64gx-mss-top-sysreg
+          - const: microchip,mpfs-mss-top-sysreg
+          - const: syscon
+          - const: simple-mfd
 
   reg:
     maxItems: 1