Don't eat extra cycles when idling.

Rescheduling between threads takes about 3000 cycles, but that's not true
for both sides of e.g. a delay.

Fixes #6409 (assuming 60fps is what a PSP gets.)
Notify the texcache when fb format changes.

Fixes #2094 again.
Fix low-level atrac3/atrac3+ decoding.

Fixes #6400.
Merge pull request #6412 from unknownbrackets/texcache

Notify the texcache when fb format changes