This mailbox hardware is present in Allwinner sun6i, sun8i, sun9i, and
sun50i SoCs. Add a device tree binding for it.
Acked-by: NMaxime Ripard <mripard@kernel.org>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NSamuel Holland <samuel@sholland.org>
Signed-off-by: NJassi Brar <jaswinder.singh@linaro.org>