dt-bindings: cpufreq: cpufreq-qcom-hw: Add missing compatibles

Document the cpufreq-epss compatibles currently used in the tree, plus
the sc7280 which will be added in a separate commit.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>