Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

This commit adds full support for USB 3.0 devices in host and device
mode in the USB core. The patch mostly consists of updating the USB
HUB code to support USB 3.0 HUBs. This patch also add some more USB
controller methods to support more active-alike USB controllers like
the XHCI which needs to be informed about various device state events.

USB 3.0 HUBs are not tested yet, due to lack of hardware, but are
believed to work.

After this update the initial device descriptor is only read twice
when we know that the bMaxPacketSize is too small for a single packet
transfer of this descriptor.

Approved by: thompsa (mentor)

Reduce the need to accesss struct usb_device by providing functions to access
the product, manufacturer and serial strings.

Submitted by: Hans Petter Selasky

- Make struct usb_xfer opaque so that drivers can not access the internals
- Reduce the number of headers needed for a usb driver, the common case is just usb.h and usbdi.h