dt-bindings: mailbox: Add APSS shared binding for SDM845 SoCs

Include SDM845 APSS shared to the list of possible bindings

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