x86/CPU/AMD: Improve the erratum 1386 workaround

Disable XSAVES only on machines which haven't loaded the microcode
revision containing the erratum fix.

This will come in handy when running archaic OSes as guests. OSes whose
brilliant programmers thought that CPUID is overrated and one should not
query it but use features directly, ala shoot first, ask questions
later... but only if you're alive after the shooting.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20240324200525.GBZgCHhYFsBj12PrKv@fat_crate.local