Start de-obfuscating the HC drivers.

Start de-obfuscating the HC drivers.

Since pipe methods have an xfer argument, always use it to get acces to
various data structure (pipe, bus, device) instead of having a different
way to get a pointer to these descriptors in every function.

Also kill the {E,U}XFER() macro and use a consistent name accross all the
methods for {e,u}hci_xfer.