MINOR: cpu-topo: use cpufreq before acpi cppc

MINOR: cpu-topo: use cpufreq before acpi cppc

The acpi_cppc method was found to take about 5ms per CPU on a 64-core
EPYC system, which is plain unacceptable as it delays the boot by half
a second. Let's use the less accurate cpufreq first, which should be
sufficient anyway since many systems do not have acpi_cppc. We'll only
fall back to acpi_cppc for systems without cpufreq. If it were to be
an issue over time, we could also automatically consider that all
threads of the same core or even of the same cluster run at the same
speed (when a cluster is known to be accurate).