dt-bindings: soc: qcom,smp2p: convert to dtschema

Convert the Qualcomm Shared Memory Point 2 Point bindings to DT Schema.

Changes against original bindings: enforce only specific names of child
nodes, instead of any names.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220411155528.502889-1-krzysztof.kozlowski@linaro.org