kernel - Refactor in-kernel system call API to remove bcopy()

kernel - Refactor in-kernel system call API to remove bcopy()

* Change the in-kernel system call prototype to take the
  system call arguments as a separate pointer, and make the
  contents read-only.

  int     sy_call_t (void *);
  int     sy_call_t (struct sysmsg *sysmsg, const void *);

* System calls with 6 arguments or less no longer need to copy
  the arguments from the trapframe to a holding structure.  Instead,
  we simply point into the trapframe.

  The L1 cache footprint will be a bit smaller, but in simple tests
  the results are not noticably faster... maybe 1ns or so
  (roughly 1%).