vl: Adjust the place of calling mlockall to speedup VM's startup

If we configure mlock=on and memory policy=bind at the same time,
It will consume lots of time for system to treat with memory,
especially when call mbind behind mlockall.

Adjust the place of calling mlockall, calling mbind before mlockall
can remarkably reduce the time of VM's startup.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>