arm64: dts: qcom: Add APSS shared mailbox node to SDM845

This patch add the node to support APSS shared
mailbox on SDM845

Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>