1. Place all frames and isoc bufs inside a dynamic region -- DONE

3. Try to replace single page vmalloc and all frames with a multi frame approach
1.1 Image buffers in a dyn region

2. Wrap struct urb inside pwc_iso as a `U inside a `RC. Need this because usb_free_urb
   is called by the driver which in effect frees the driver.

4. Try using non tag_t dependent types -- need this for usb_endpoint_descriptor 
  which uses a packed u8 for a length field

5. Problem with dependent type for
transfer_buffer/transfer_buffer_length and `RC pointer
... again. Additional trouble because the interface is controlled by
usb.h. Can't change the representation. Need a stronger unpack construct!
