c/s 9b23cfb7

or

c/s b154537a

moved the testing of xen_enabled() from pc_init1() to
pc_machine_initfn().

xen_enabled() does not return the correct value in
pc_machine_initfn().

Changed vmport from a bool to an enum.  Added the value "auto" to do
the old way.  Move check of xen_enabled() back to pc_init1().
Acked-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NDon Slutz <dslutz@verizon.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>