[Nouveau] vp3 hang on mplayer exit (for GT240 videocard) - workaround found?

[Andrew Randrianasulu]

Apparently, this hang can be fixed at small performance cost by setting

NOUVEAU_VP3_DEBUG_FENCE 1 (as opposed to default 0)
in https://cgit.freedesktop.org/mesa/mesa/tree/src/gallium/drivers/nouveau/nouveau_vp3_video.h

Now, what exactly fixes my hangs (or make them less severe) - still open question, 
guess I can flip few of those debug defines and try to find out ...

Currently at mesa Mesa 20.3.0-devel (git-8557b1a8eb)

I can launch two of those VIDEO:  [H264]  1920x1080  0bpp  59.940 fps and it will not hang
Even survived 5 x 1080p h264 (30 fps) videos - it was slideshow (due to DRI_PRIME ?)
but it does not hang ....