dt-bindings: mailbox: apple,mailbox: Add t8112 compatibles

The mailbox hardware remains unchanged on M2 SoCs so just add its
per-SoC compatible.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Janne Grunau <j@jannau.net>
Signed-off-by: Hector Martin <marcan@marcan.st>