x86/cpufeatures: Add X86_FEATURE_XENPV to disabled-features.h

Add X86_FEATURE_XENPV to the features handled specially in
disabled-features.h.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/r/20221104072701.20283-2-jgross@suse.com