dt-bindings: mailbox: qcom,apcs-kpss-global: Document the qcs615 APSS

Add compatible for the Qualcomm qcs615 mailbox block.
QCS615 mailbox is compatible with SDM845 use fallback for it.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Kyle Deng <quic_chunkaid@quicinc.com>
Link: https://lore.kernel.org/r/20241018073417.2338864-2-quic_chunkaid@quicinc.com


Signed-off-by: Rob Herring (Arm) <robh@kernel.org>