dt-bindings: mailbox: Document Hi6220 mailbox driver

Document DT binding for Hisilicon Hi6220 mailbox driver.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
1 file changed