dt-bindings: mailbox: fix the mpfs' reg property

The "data" region of the PolarFire SoC's system controller mailbox is
not one continuous register space - the system controller's QSPI sits
between the control and data registers. Split the "data" reg into two
parts: "data" & "control".

Fixes: 21355623 ("dt-bindings: soc/microchip: update syscontroller compatibles")
Fixes: ed9543d6 ("dt-bindings: add bindings for polarfire soc mailbox")
Reviewed-by: NKrzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: NConor Dooley <conor.dooley@microchip.com>
Signed-off-by: NJassi Brar <jaswinder.singh@linaro.org>

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

@@ -14,9 +14,15 @@ properties:
     const: microchip,mpfs-mailbox
 
   reg:
-    items:
-      - description: mailbox data registers
-      - description: mailbox interrupt registers
+    oneOf:
+      - items:
+          - description: mailbox control & data registers
+          - description: mailbox interrupt registers
+        deprecated: true
+      - items:
+          - description: mailbox control registers
+          - description: mailbox interrupt registers
+          - description: mailbox data registers
 
   interrupts:
     maxItems: 1
@@ -39,7 +45,8 @@ examples:
       #size-cells = <2>;
       mbox: mailbox@37020000 {
         compatible = "microchip,mpfs-mailbox";
-        reg = <0x0 0x37020000 0x0 0x1000>, <0x0 0x2000318c 0x0 0x40>;
+        reg = <0x0 0x37020000 0x0 0x58>, <0x0 0x2000318C 0x0 0x40>,
+              <0x0 0x37020800 0x0 0x100>;
         interrupt-parent = <&L1>;
         interrupts = <96>;
         #mbox-cells = <1>;