dt-bindings: firmware: document Qualcomm SM6115 SCM

Document the compatible for Qualcomm  SM6115 SCM.

Signed-off-by: Adam Skladowski <a39.skl@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220815100952.23795-8-a39.skl@gmail.com