x86/pti: Add attack vector controls for PTI

Disable PTI mitigation if user->kernel attack vector mitigations are
disabled.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250707183316.1349127-20-david.kaplan@amd.com