x86/bugs: Define attack vectors relevant for each bug

Add a function which defines which vulnerabilities should be mitigated
based on the selected attack vector controls.  The selections here are
based on the individual characteristics of each vulnerability.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250707183316.1349127-5-david.kaplan@amd.com