Add support for the spice tablet interface. The tablet interface will
be registered (and then used by the spice client) as soon as a absolute
pointing device is available and used by the guest, i.e. you'll have to
configure your guest with '-usbdevice tablet'.
With that patch applied you'll actually see the guests screen in the
spice client. This does *not* bring qxl and full spice support though.
This is basically the qxl vga mode made more generic, so it plays
together with any qemu-emulated gfx card. You can display stdvga or
cirrus via spice client. You can have both vnc and spice enabled and
clients connected at the same time.