supervisor/pager: Extract new function, FLUSH-TLB.
supervisor/pager: Extract new function, FLUSH-TLB.

  * Rather than comment on what an opaque manipulation of some
system register does, extract the function so that we have a name
for the operation.  Then explain WHY the manipulation is correct,
rather than relying on a reader's intimate knowledge of x86oid
paged memory management.

varjagg/Mezzano,varjagg/Mezzano,rvedam/Mezzano,froggey/Mezzano,froggey/Mezzano,AugustusHuang/Mezzano,AugustusHuang/Mezzano,rvedam/Mezzano