i386: Add EPYC-IBPB CPU model
    
    EPYC-IBPB is a copy of the EPYC CPU model with
    just CPUID_8000_0008_EBX_IBPB added.
    
    Cc: Jiri Denemark <jdenemar@redhat.com>
    Cc: Tom Lendacky <thomas.lendacky@amd.com>
    Cc: Brijesh Singh <brijesh.singh@amd.com>
    Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
    Message-Id: <20180109154519.25634-7-ehabkost@redhat.com>
    Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
    (cherry picked from commit 6cfbc54e8903a9bcc0346119949162d040c144c1)
    Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>