Fix USB hotplug on type-C connectors of Apple Silicon hardware. The USB

Fix USB hotplug on type-C connectors of Apple Silicon hardware.  The USB
controller on these machines does not see connection events.  Instead we
need to rely on the USB PD controllers to notify us of a new connection
and reset the USB controller.  This diff implements this by adding a new
tipd(4) driver and infrastructure to notify xhci(4) of new connections.

ok patrick@