Fixup gsp synch

Fixes issues with GSP synchronization. This is mostly experimental work that has been a result of trial and error, so I can't guarantee accuracy. However, I can assert the following:
* All known applications that worked (to my knowledge) still work
* Fixes the loading animation in Cubic Ninja
* Cave Story 3D runs 10X faster, and gets past the opening logos
* Other games (while not showing additional gfx) seem to no longer hang (e.g. Cubic Ninja, Cave Story 3D, Reto City Rampage)
This `static` usage is terrible for determinism when starting another game once emulation has finished (i.e. the startup state for the second session will not be the same as in the initial state). Since the affected code signalizes an interrupt, this might very well introduce chances for random-freezes. Hence, please change to a file-global var.