Eat cycles when context switching and delaying

Testing it carefully on a PSP, I found that I could not get any scheduling to happen in the <= 1us PPSSPP gave.  These changes make it take time, which fixes some issues I hit trying to improve callbacks.

This could affect timing and speed in some games, so it's probably good to test.  I want to do this before the other callback changes to be safe.

-[Unknown]