Use kvm acceleration if available.
Disable kernel-irqchip and use qemu64 cpu
for both kvm and tcg cases.
Using kvm acceleration saves about a second
and disabling kernel-irqchip has no visible
performance impact.
Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Marcel Apfelbaum <marcel@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>