Currently we have two conflicting definitions of struct usb_config_descriptor
and struct usb_interface_descriptor in the tree. This is because the USB code
uses additional fields in the structs for internal housekeeping. Add
struct usb_interface and struct struct usb_configuration with the housekeeping
data and embed the corresponding hardware structs into them. This frees the
way to use the definitions from ch9.h in the next step.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>