Improve readdir speed

[fjtrujy]

Pull Request checklist

Note: these are not necessarily requirements

• I reformatted the code with clang-format
• I checked to make sure my submission worked
• I am the author of submission or have permission from the original author
• Requires update of the PS2SDK or other dependencies
• Others (please specify below)

Pull Request description

This PR basically makes the readdir function to work faster, as it doesn't require anymore to run stat function to identify if it is or not a folder/file.
stat function is an expensive call, skipping it we are going to have a much faster game/app listing.

Cheers.