New microcode introduces the "Speculative Store Bypass Disable"
CPUID feature bit. This needs to be exposed to guest OS to allow
them to protect against CVE-2018-3639.
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>
Reviewed-by: NJiri Denemark <jdenemar@redhat.com>
(cherry picked from commit 1dbca2ec)