dt-bindings: mailbox: qcom,apcs-kpss-global: use fallbacks

Rework the compatibles and group devices which have similar interface
(same from Linux driver point of view) as compatible.  This allows
smaller of_device_id table in the Linux driver and smaller
allOf:if:then: constraints.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>