dt-bindings: cpufreq: qcom-hw: add a compatible for sa8775p

Add the compatible for the cpufreq engine present on sa8775p platforms.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>