bhyve: use speed in hci to allow backend modify it.

[aokblast]

Summary

The speed of usb device may be setup dynamically by the backend. For
example, the usb device passthrough relies on the internal device to
provide the speed correctly. Therefore, instead of initialize the device
from the ue information statically, we provide the speed from the
usb_hci. At the same time, when the backend does not provide the speed,
we fallback to the speed in the ue structure.

Sponsored By: The FreeBSD Foundation

[markj]

Approved