xhci: Better debugging for critical host errors.

xhci: Better debugging for critical host errors.

When a host controller gives a bad event TRB, we should print out the
contents of the TRB as a warning so that users don't have to recompile
their kernel to get information about what went wrong.  Also, print out
the event ring if they have xHCI debugging turned on, since previous
events can often explain what happened before the bad TRB occurred.

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