arm64: dts: sc7180: Add cpufreq HW node for cpu scaling

cpufreq hw node required to scale CPU frequency on sc7180.

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Taniya Das <tdas@codeaurora.org>
Link: https://lore.kernel.org/r/0101016ed02b6356-5165eaaa-6c54-47ff-a008-821c91831e56-000000@us-west-2.amazonses.com


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>