Frequency-invariant utilization tracking for x86

There was a patch[1] a few months ago, submitted by an AMD employee, trying to add CPPC2 awareness to the ondemand governor. It was rejected (rightly so IMO) for ignoring schedutil entirely and adding far too many knobs; the existing AMD CPB subdriver (which also ignores schedutil) only needs one boolean.

On some of the older CPUs I have there's also a 100mhzsteps feature flag in /proc/cpuinfo, I don't know if it's just not worth the effort or if nobody ever wrote the code to support it. The ACPI cpufreq driver definitely doesn't have 100MHz granularity.

[1]: https://lkml.org/lkml/2019/7/10/682