Improve performance of the GE list interpreter

This adds a `FastRunLoop()` to GPU_GLES and NullGPU.

It has the following benefits:
 * stall and gpuState aren't both checked, instead just a downcount.
 * when debugging features (like dump frame) are enabled, runs `SlowRunLoop()`, so those can be near-free without compile flags.
 * runs `PreExecuteOp()` much faster since it isn't a virtual call.

This wasn't really a bottleneck, but it was showing up in some profiles (mostly for games that already run faster.)  With this change, Lunar and Unchained Blades for example gain 5% performance.

LittleBigPlanet, Final Fantasy Type-0, Tales of Eternia, etc. aren't really affected (well might be, but a tiny bit.)

-[Unknown]