multimedia/vapoursynth: Limit port to tier 1 (64-bit) platforms and fix some style issues

Upstream only targets 64-bit platforms
(see release notes for R74 and meson.build) and they're the only plugins
are only optimized and/or runs reasonably fast on aarch64 and amd64.
This is also true for most other related software you normally use with
Vapoursynth. While at fix a few style issues