qemu: assume QEMU_CAPS_VIRTIO_PACKED_QUEUES

qemu: assume QEMU_CAPS_VIRTIO_PACKED_QUEUES

Added by QEMU commit:

commit 74b3e46630446568aecb0be1c77c4875d7a52f6d
Author:     Jason Wang <jasowang@redhat.com>
CommitDate: 2019-10-25 07:46:22 -0400

    virtio: add property to enable packed virtqueue

    Signed-off-by: Jason Wang <jasowang@redhat.com>
    Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
    Reviewed-by: Jens Freimann <jfreimann@redhat.com>
    Message-Id: <20191025083527.30803-9-eperezma@redhat.com>
    Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
git describe: v4.1.0-1780-g74b3e46630 contains: v4.2.0-rc0~32^2~17

Signed-off-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>