xhci: trace debug statements for urb cancellation

This patch defines a new trace event, which is called xhci_dbg_cancel_urb
and belongs to the event class xhci_log_msg, and adds tracepoints that
trace the debug messages related to the removal of a cancelled URB from
the endpoint's transfer ring.

Signed-off-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>