Option to create only vertical configs

[Andrew-H2O]

The default config probably does a good enough job for horizontal games. Is it worth adding the option to only generate configs for vertical games?

[dankcushions]

The default config in retropie is no shaders, but instead of creating per-game overrides, we could instead create a single core override for vertical games (which simply turns the crt-pi shader on), and then use the per-rom cfgs for all the vertical games.

however maybe it's easier for users to maintain/understand if we stick to current per-game system. i would suggest that horizontal games don't hardcode the viewport via the generate .cfg, since they're the same as the default anyway.