[F.Rq.] Expose Blargg NTSC filter in Genplus-gx

Expose blarrg ntsc filter setting under core settings for gens plus gx.

[YoshiRulz]

This looks like a post-processing filter (shader), which is a frontend concern. You can load custom shaders under Config > Display..., though not all shaders will work. Blargg's definitely won't work because it's not really a shader—it's a library which is compiled in, and runs on the CPU according to the readme here.

The core has this built in tho but ok