arm64: dts: qcom: sc7280: Add cpufreq hw node

Add cpufreq HW device node to scale 4-Silver/3-Gold/1-Gold+
cores on SC7280 SoCs.

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Taniya Das <tdas@codeaurora.org>
Link: https://lore.kernel.org/r/1618020280-5470-2-git-send-email-tdas@codeaurora.org
[bjorn: Dropped reg-names]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>