dt-bindings: cpufreq: cpufreq-qcom-hw: add SDM670 compatible

The bindings for Qualcomm CPU frequency have a compatible for each SoC.
Add the compatible for SDM670.

Fixes: 0c665213

 ("arm64: dts: qcom: sdm670: add cpu frequency scaling")
Signed-off-by: Richard Acayan <mailingradian@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>