mbox: qcom: add APCS child device for QCS404

There is clock controller functionality in the APCS hardware block of
qcs404 devices similar to msm8916.

Co-developed-by: Niklas Cassel <niklas.cassel@linaro.org>
Signed-off-by: Niklas Cassel <niklas.cassel@linaro.org>
Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>