CAV disc drive

Changes the read speed of GC discs from 3 MiB/s to 2-3.3 MiB/s,
depending on the location of the data. I also attempted to change the
speeds for Wii discs, but it has very little effect right now because
Wii games use IPC_HLE instead of DVDInterface. It does affect Wii
homebrew that reads Wii discs, though.