This reimplements the USB HID v4 IOS device using the new common
USB code (to reuse more code and allow emulated HIDs to be added
more easily in the future).
The main difference is that HIDs now have to be whitelisted, like
every other USB device for OH0 and VEN.
IPC_HLE is actually IOS HLE. The actual IPC emulation is not in
IPC_HLE, but in HW/WII_IPC.cpp. So calling IPC_HLE IOS is more
accurate. (If IOS LLE gets ever implemented, it'll likely be at
a lower level -- Starlet LLE.)
This also totally gets rid of the IPC_HLE prefix in file names, and
moves some source files to their own subdirectories to make the file
hierarchy cleaner.
We're going to get ~14 additional source files with the USB PR,
and this is really needed to keep things from becoming a total pain.
