usb: host: xhci: add xhci_virt_device tracer

Let's start tracing at least part of an xhci_virt_device lifetime. We
might want to extend this tracepoint class later, but for now it already
exposes quite a bit of valuable information.

Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>