vaapipluginutil: Use GST_VAAPI_DISPLAY_TYPE_DRM for Mesa3D GBM
vaapipluginutil: Use GST_VAAPI_DISPLAY_TYPE_DRM for Mesa3D GBM

We may build this plugin with window system support but run it without
window system. Without this patch, the following pipeline will trigger a
segfault when running it without window system.

gst-launch-1.0 filesrc location=input.264 ! h264parse ! vaapih264dec ! fakesink

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer-vaapi/-/merge_requests/319>

GStreamer/gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi,ceyusa/gstreamer-vaapi