dt-bindings: firmware: document Qualcomm SC8180X SCM

Document the compatible for Qualcomm sc8180x SCM.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230325122444.249507-2-vkoul@kernel.org