dt-bindings: firmware: qcom,scm: add qcom,scm-sa8775p compatible

Add a compatible for the sa8775p platform's Secure Channel Manager
firmware interface.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230127192139.299228-1-brgl@bgdev.pl