Move inappropriate stuff in cpu.h elsewhere:
{s,g}et_intr_mask -> md_var.h
num_tlbentries -> tlb.h
Remove #define clockframe trapframe and fix clock, which was the only place
this was used.
All the rest of this stuff was unused.
# we're not quite minimal yet, since we duplicate a few status register things
# here...
Inspired by: bde@