kernel - 64-bit memory & ncpus work

kernel - 64-bit memory & ncpus work

* Create a macro and bsr function for cpu masks in preparation for
  making cpumask_t 64 bits on 64-bit builds.  cpumask_t is still
  32 bits in this commit.

* Expand SMP_MAXCPUS to 31 for 64-bit builds in preparation for
  eventually expanding it to 63.

* Fix an array overflow when probing ncpus on 64-bit.

* Increase the boot-time kmap entries to accomodate large numbers of
  cpus.

* Clean up a few places where integer overflows could occur on
  64-bit machines with large amounts of ram.

  For the moment we are limited to 32G.  This will change in a
  followup commit.