Fix some more GPU thread sync issues

Mostly I was trying to hunt for a very random and hard to repro hang I'm getting in Tales of Phantasia X.  I'm not sure if I got it...

Anyway, this fixes a problem with the dirty FB check skipping way too many frames, since it didn't give the GE time to finish.  Should not hurt performance, and fixes at least God Eater Burst.

-[Unknown]