Reimplement "kernel_pmap" in the standard way.
Eliminate unused variables. (These are mostly variables that were
discarded by the machine-independent layer after FreeBSD 4.x.)
Properly handle a vm_page_alloc() failure in pmap_init().
Eliminate dead or legacy (FreeBSD 4.x) code.
Eliminate unnecessary page queues locking.
Eliminate some excess white space.
Correct the synchronization of pmap_page_exists_quick().
Tested by: gonzo
