qxl: add QXL_IO_MONITORS_CONFIG_ASYNC

qxl: add QXL_IO_MONITORS_CONFIG_ASYNC

Revision bumped to 4 for new IO support, enabled for spice-server >=
0.11.1. New io enabled if revision is 4. Revision can be set to 4.

[ kraxel: 3 continues to be the default revision.  Once we have a new
          stable spice-server release and the qemu patches to enable
          the new bits merged we'll go flip the switch and make rev4
          the default ]

This io calls the corresponding new spice api
spice_qxl_monitors_config_async to let spice-server read a new guest set
monitors config and notify the client.

On migration reissue spice_qxl_monitors_config_async.

RHBZ: 770842

Signed-off-by: Alon Levy <alevy@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
fixup

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>