Make file open timing a bit more accurate

[unknownbrackets]

I think this will help #6582.

This makes filesystems expose flags indicating UMD/CARD/FLASH to make it easier to deviate timing depending on what's mounted. PBPs are treated as CARD while ISOs are treated as UMD.

Also, I found that PSP OFW allows enabling/disabling the UMD cache, but CFW disables it anyway for homebrew. In the past have seen some timing using JpcspTrace/etc. but gonna need to find a better way...

This mostly aims for the mid-fast end of actual timing metrics. There are some differences from observed reality:

• If the UMD spins down, Open/OpenAsync could take 1.5s or so, but mainly not found ones (I think it caches the path table even without cache, not sure.)
• Uses 4ms (low end average of many runs) for UMD open, but it can be as fast as 1.2ms without cache.
• Didn't have a great way to carefully time with cache.
• Memory Stick access should get slower (around 0.8ms per path component) for deeper files, but there's also clearly a file table cache that makes this faster after first access.
• Didn't test nocwd or other less common errors.

-[Unknown]

[hrydgard]

Very nice! This one we'll definitely do after 1.10 though, indeed.