dt-bindings: mailbox: Add YAML schemas for QCOM APCS global block

Qualcomm APCS global block provides a bunch of generic properties which
are required in a device tree. Add YAML schema for these properties.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sivaprakash Murugesan <sivaprak@codeaurora.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>