x86/CPU/AMD: Disable INVLPGB on Zen2

In the Linux kernel, the following vulnerability has been resolved:

x86/CPU/AMD: Disable INVLPGB on Zen2

AMD Cyan Skillfish (Family 17h, Model 47h, Stepping 0h) has an issue that causes system oopses and panics when performing TLB flush using INVLPGB.

However, the problem is that that machine has misconfigured CPUID and should not report the INVLPGB bit in the first place. So zap the kernel's representation of the flag so that nothing gets confused.

[ bp: Massage. ]