USB4BSD (USB2): How do I activate and use the new USB infrastructure?

For those with us having missed how to use the new USB2 stuff:

How do I use the new USB4BSD stuff? What is necessary in kernel config?
I tried to load everything beginning with 'usb2_...' via loader.conf (no
device usb... in kernel config), but no USB device was recognized after
that, especially no mice. So I guess I forgott the basic/primary USB2
infrastructure 'device' in kernel config. Can someone give me a hint
were to read about this?

Thanks a lot.

Oliver