dt-bindings: cpufreq: cpufreq-qcom-hw: Document Qcom EPSS compatible

The hardware block which carries out CPUFreq operations on SM8250 SoC is
called EPSS. Hence, document the compatible.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Amit Kucheria <amitk@kernel.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>