Disc drive unification (make WII_IPC_HLE_Device_DI call DVDInterface)

The main purpose of this change is to make Wii games use the accurate disc drive speeds that have been implemented in DVDInterface. It also improves compatibility with Wii software that interfaces with DI directly - most notably, CleanRip will now be able to read past the 4 GiB mark on Wii discs. (I don't know if CleanRip can dump Wii games properly yet, though.) As a bonus, Wii games now support the fast disc speed option.