* if downstream provides us with a pool that can allocate DMA buffers,
gldownload wraps it into a GL buffer pool that uses
glEGLImageTargetTexture2DOES() to import dmabuf into textures
* upstream GL elements can allocate from that pool
* gldownload unwraps DMA buffers from incoming GL buffers and passes
them downstream
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6792>