Emulate GameCube memory card speeds

Fixes http://code.google.com/p/dolphin-emu/issues/detail?id=2284

Attempts to emulate GameCube memory card transfer speeds.

Wind Waker J has been tested and confirmed working with this by JMC47
Have these been timed on hardware or are they guesses based on more "synthetic" timing (like measuring the time taken by a game to save data)? It would be useful to add this information in the comment.