obs-ffmpeg: Implement NVENC video card blacklist

This implements a blacklist of devices that ship with NVENC libraries,
but do not support NVENC, which would cause the plugin to mistakenly
think that NVENC was available when it was not.  If these devices are
the only NVIDIA devices on the system, consider NVENC unavailable.

This is much more efficient than spawning an encoder on startup to see
if NVENC is available, which would incur a ~500 millisecond hit on
startup.  Additionally, also much less crash-prone.