Document the compatible for the QDU1000 mailbox.
Signed-off-by: Melody Olvera <quic_molvera@quicinc.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>