Create the cheats directory always.

Seems like things break otherwise?  Fixes #4169.
Allow cheats to start and stop in game.
Let's just always use PSP/Cheats/, it's simpler.

No reason people on iOS won't want this.
Don't require reset to enable cheats.
Don't crash if the cheat file is inaccessible.
Also allow restartless cheats after loading state.

At least, an older state.
Merge pull request #4170 from unknownbrackets/cheats

Fix cheats on a default install, remove restart game requirement