backends/drm: disable triple buffering on NVidia

Xaver Huglrequested to merge
work/zamundaaa/nv-glitches into Plasma/6.1

Until we figure out what's wrong, it's best to leave it disabled. I'm only targeting 6.1 because it seems to be a driver bug that'll hopefully be resolved before 6.2

BUG: 487833

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