Added intel_recommended_pstate builtin function.

What?

Added intel_recommended_pstate builtin function which reads the processor name from pmu file under /sys/devices, and returns correct pstate value.

Why?

Intel recommends to use the intel_pstate CPUFreq driver in active mode with HWP enabled on Ice Lake and later generations processors.This feature allows dynamically setting intel_pstate based on the processor's model. Currently, users need to create a tuned override if they want to set intel_pstate to active even for newer generation processors. For older generation processors setting pstate to active can introduce jitters which were historically seen around and tested with RHEL-7.4.From IceLake generation, intel has fixed these issues.

How this works?

With this builtin function it is possible to write now:
```
[variables]
pstate=${f:intel_recommended_pstate}
```

[bootloader] cmdline_pstate=+intel_pstate=${pstate}


 The builtin function will return value: disable|active based on the processor model and pass the proper intel_pstate value to kernel command line in boot time. The return values are stricter to only disable and active

redhat-performance / tuned