the device driver instead of happening automagically in the HC driver.
This affects both the HC-USBD interface as well as the USBD-device
interface.
This change will allow DMA buffers to be reused e.g. in isochronous
traffic.
Add isochronous support to the UHCI driver (not for OHCI yet).
It is accessible through the usual tty abstraction.
XXX The driver needs better error handling and a special call device.
XXX It also needs more testing.