Fix threadsPerCore check for Zen 2 (AMD)

[maksimio]

Hello @klauspost, thanks for the library! I tried running it on my CPU Ryzen 5 4500u (Zen2) and found that the number of threads per core (2) and physical cores (3) were incorrect and the HTT option was also detected incorrectly. In fact this cpu has 1 thread per core and 6 physical (and logical) cores

I wrote a fix using the PPR for AMD Family 17h Models 00h-0Fh Processors (page 82)

You can find CPUID dump of Ryzen 5 4500u here

[klauspost]

Great find! While unlikely to ever be hit, I'd propose this as a conservative approach.

Something VM's can be a bit finicky and filter CPUID values.