virtio: make virtio device's structures public.

virtio: make virtio device's structures public.

These structures must be made public to avoid two memory allocations for
refactored virtio devices.

Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Message-id: 1363624648-16906-2-git-send-email-fred.konrad@greensocs.com

Changes V4 <- V3:
   * Rebased on current git.

Changes V3 <- V2:
    * Style correction spotted by Andreas (virtio-scsi.h).
    * Style correction for virtio-net.h.

Changes V2 <- V1:
    * Move the dataplane include into the header (virtio-blk).
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>