mailbox: Add support for Qualcomm SDM845 SoCs

Add the corresponding APSS shared offset for SDM845 SoC

Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>