Drop the old SysBus init function and use instance_init

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: xiaoqiang zhao <zxq_yx_007@163.com>
Message-id: 1463111220-30335-2-git-send-email-zxq_yx_007@163.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>