ARM: dts: qcom: sdx55: Add CPUFreq support

Add CPUFreq support to SDX55 platform using the cpufreq-dt driver.
There is no dedicated hardware block available on this platform to
carry on the CPUFreq duties. Hence, it is accomplished using the CPU
clock and regulators tied together by the operating points table.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>