dt-bindings: mailbox: Add Apple M3 (t8122) compatible

The mailbox on M3 (t8122) is compatible with asc-mailbox-v4,
so add the t8122 compatible variant to enum section of the v4
mailbox section.

Signed-off-by: Michael Reeves <michael.reeves077@gmail.com>

Author: IntegralPilot

Documentation/devicetree/bindings/mailbox/apple,mailbox.yaml

@@ -30,6 +30,7 @@ properties:
           - enum:
               - apple,t8103-asc-mailbox
               - apple,t8112-asc-mailbox
+              - apple,t8122-asc-mailbox
               - apple,t6000-asc-mailbox
               - apple,t6020-asc-mailbox
           - const: apple,asc-mailbox-v4