i386: Add FEAT_8000_0008_EBX CPUID feature word
    
    Add the new feature word and the "ibpb" feature flag.
    
    Based on a patch by Paolo Bonzini.
    
    Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
    Message-Id: <20180109154519.25634-5-ehabkost@redhat.com>
    Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
    (cherry picked from commit 1b3420e1c4d523c49866cca4e7544753201cd43d)
    Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>