WII_IPC_HLE: Return delay time instead of using GetCmdDelay
WII_IPC_HLE: Fix timing weirdness

This change makes it very noticable that DI uses the slow speed of
about 1 MB/s. The DI speed will be fixed in the next commit.
Make WII_IPC_HLE_Device_DI call DVDInterface
WII_IPC_HLE_Device_DI: Implement fast disc speed option

Works like the DVDInterface fast disc speed, except it schedules
a response after 1 tick instead of replying immediately.
DVDInterface: Tweak speeds