[PATCH 2/3] dt-bindings: mailbox: Add Apple mailbox bindings

[Alyssa Rosenzweig]

> +      - description:
> +          M3 mailboxes are an older variant with a slightly different MMIO
> +          interface still found on the M1.
> +        items:
> +          - const: apple,t8103-m3-mailbox

Would be nice to document an example of where an M3 mailbox is found.

> +  interrupts:
> +    minItems: 4
> +    items:
> +      - description: send fifo is empty interrupt
> +      - description: send fifo is not empty interrupt
> +      - description: receive fifo is empty interrupt
> +      - description: receive fifo is not empty interrupt
> +
> +  interrupt-names:
> +    minItems: 4
> +    items:
> +      - const: send-empty
> +      - const: send-not-empty
> +      - const: recv-empty
> +      - const: recv-not-empty

If the names became not-constant the asprintf thing goes away, not sure
that's better or worse.

> +  clocks:
> +    description:
> +      Reference to the clock gate phandle(s) if required for this mailbox.
> +      Optional since not all mailboxes are attached to a clock gate.

Do we do anything with the clocks at this point?