Apply a hack to simulate USB created files

[unknownbrackets]

Fixes #9794. Some homebrew accidentally depend on a PSP firmware bug. It happens to be the same flaw Windows 98 has, for exactly the same reason.

Since I was moving it away from affecting case-sensitive ISO filesystems, I tested quickly to verify it's the same Windows 98 bug (as described in #9793) and made it follow the basename/extension logic correctly. I could see some homebrew also mishandling "data.BIN" (which NT/XP/7/8/10/etc. would write as "DATA.BIN + lowercase basename flag".)

Note that the PSP also doesn't write this flag. The danger here would be:

1. A game writes save data with a lowercase filename, i.e. "data.bin".
2. The game then reads back the directory listing immediately.
3. The game expects to see "data.bin" (as it would on a real PSP) instead of "DATA.BIN".

But note that the savedata code skips files that are not all uppercase in FILES, and almost all games write uppercase. So hopefully the above scenario is very unlikely.

Otherwise we'd have to track lowercase filenames written since game start, or something. Or just only apply this hack when running homebrew.

-[Unknown]

[BenMcLean]

Thanks for making this.