Change USB over to make_dev() for all device nodes, previously it hooked into

Change USB over to make_dev() for all device nodes, previously it hooked into
the devfs clone handler to open the (invisible) devices on the fly.

The /dev entries are layed out as follows,

 /dev/usbctl      = master device
 /dev/usb/0.1.0.5 = usb device, (<bus>.<dev>.<iface>.<endpoint>)
 /dev/ugen0.1 -> usb/0.1.0.0 = ugen link to ctrl endpoint

This also removes the custom permissions model from USB.  Bump
__FreeBSD_version to 800066.

Submitted by:	rink (earlier version)