dt-bindings: remoteproc: qcom,smd-edge: define re-usable schema for smd-edge

'smd-edge' property appears in multiple bindings, so split it into one
place which can be re-used.  This reduces code duplication and adds
strict schema matching for smd-edge nodes (instead of just
"type:object").

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220517070113.18023-9-krzysztof.kozlowski@linaro.org