vaapipostproc: add support for GLTextureUploadMeta output.
vaapipostproc: add support for GLTextureUploadMeta output.

This allows for vaapipostproc to be chained to the glimagesink element
for instance.

https://bugzilla.gnome.org/show_bug.cgi?id=735231

gbeauchesne/gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,CapOM/gstreamer-vaapi,ceyusa/gstreamer-vaapi,GStreamer/gstreamer-vaapi,CapOM/gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,CapOM/gstreamer-vaapi