Make gst_vaapi_display_get_display_type() return the actual VA display
type. Conversely, add a gst_vaapi_display_get_class_type() function to
return the type of the GstVaapiDisplay instance. The former is used to
identify the display server onto which the application is running, and
the latter to identify the original object class.
This patch updates to relect the 1.0 version of the protocol. The main
changes are the switch to wl_registry for global object notifications
and the way that the event queue and file descriptor is processed.
Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>