Ivy Bridge Power Management on Big Sur

I have a Dell laptop with an Intel i5-3337U. Power Management works correctly on Mojave with SMBIOS set to `MacBookAir5,2` and `SSDT-PM.aml` generated by ssdtPRGen (I had to use the options `-lfm 800 -c 2` otherwise the following panic happens: `P-state Stepper Error 18 at Step 29 in context 2 on CPU 0`).

To upgrade to Big Sur the SMBIOS `MacBookAir5,2` is no longer valid. As there are no longer any laptop Ivy Bridge SMBIOS available I switched to the next closest: `MacBookAir6,2` while still keeping `SSDT-PM.aml`. At first it seemed that Power Management was still working, IORegistryExplorer showed exactly as the "Power Management Working" screenshot (which contradict the caption "XCPM Present" as there is no xcpm for Ivy Bridge).

However, upon further inspection Power Management was not working correctly at all. In Intel Power Gadget the `CORE AVG` frequency was not (closely) following the `CORE REQ` frequency as it was before on Mojave with `MacBookAir5,2`. The `CORE REQ` frequency was stuck on the ~2.6 Ghz. But the biggest problem was that after waking from sleep performance was ~33% lower than before sleep. I tested this with WebGL Aquarium in Safari (5000 fish): after a fresh boot the fps was about ~24fps, after a sleep/wake it was ~15fps.

To fix Power Managent on Big Sur I used CPUFriend to inject the properties of `MacBookAir5,2` while still retaining SMBIOS `MacBookAir6,2`. I used the ResourceConverter.sh from CPUFriend to convert the `MacBookAir5,2` plist (`/System/Library/Extensions/IOPlatformPluginFamily.kext/Contents/PlugIns/X86PlatformPlugin.kext/Contents/Resources/Mac-2E6FAB96566FE58C.plist`) to `cf-frequency-data` and added this to `SSDT-PM.aml`. (I used Mojave as source for the plist, but later I saw that it was still available in Big Sur)

After this Power Managment is working correctly on Big Sur with SMBIOS `MacBookAir6,2` like it was on Mojave with SMBIOS `MacBookAir5,2`.

I would suggest the following things for the guides:
- Add a section to the Power Managment guide (for Ivy/Sandy? Bridge) explaining injecting power properties from the closest matching SMBIOS with CPUFriend when that SMBIOS is no longer supported.
- Mention this in OpenCore and macOS 11: Big Sur
- Mention this in OpenCore For Legacy Macs sections
- Maybe add this to Opencore-Legacy-Patcher?
- In the Power Managment guide there is a caption on the IORegistryExplorer screenshot that reads "Power Management Working" and "XCPM Present", this is not (always) correct: alter/clarify this.