libqos: access VIRTIO 1.0 vring in little-endian

libqos: access VIRTIO 1.0 vring in little-endian

VIRTIO 1.0 uses little-endian for the vring.  Legacy VIRTIO uses guest
endianness.  Adjust the code to handle both.

Note that qvirtio_readq() is not defined because it has no users.  All
the other accessors are really needed.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20191023100425.12168-10-stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>