qxl: async io support using new spice api

qxl: async io support using new spice api

Some of the QXL port i/o commands are waiting for the spice server to
complete certain actions.  Add async versions for these commands, so we
don't block the vcpu while the spice server processses the command.
Instead the qxl device will raise an IRQ when done.

The async command processing relies on an added QXLInterface::async_complete
and added QXLWorker::*_async additions, in spice server qxl >= 3.1

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