dprint is still used for qxl_init_common one time prints.

also switched parts of spice-display.c over, mainly all the callbacks to
spice server.

All qxl device trace events start with the qxl device id.
Signed-off-by: NAlon Levy <alevy@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>