kernel - Reduce BSS size (2)

kernel - Reduce BSS size (2)

* Fix a bunch of other places in the kernel where large BSS arrays are
  declared.  Reduces the kernel image by another ~2MB or so on top of
  the ~6MB saved in the last commit.

* Primarily these are places where a 'struct thread' is being embedded
  in a structure which is being declared [MAXCPU].  With MAXCPU at 256
  the result is pretty bloated.  Changing the embedded thread to a
  thread pointer removes most of the bloat.