This updates the ehci periodic schedule dumping code to be
more useful when displaying the interrupt transfer tree:

  - includes start/complete split frame mask in QH
  - gets rid of some needless output (more terse)
  - shows whether IN or OUT tds are queued, and how many

The microframe info isn't yet very interesting, but it's
helpful when a microframe scheduler is in use.  (Which will
be a patch some other time!)