kernel - Add support for up to 63 cpus & 512G of ram for 64-bit builds.

kernel - Add support for up to 63 cpus & 512G of ram for 64-bit builds.

* Increase SMP_MAXCPU to 63 for 64-bit builds.

* cpumask_t is 64 bits on 64-bit builds now.  It remains 32 bits on 32-bit
  builds.

* Add #define's for atomic_set_cpumask(), atomic_clear_cpumask, and
  atomic_cmpset_cpumask().  Replace all use cases on cpu masks with
  these functions.

* Add CPUMASK(), BSRCPUMASK(), and BSFCPUMASK() macros.  Replace all
  use cases on cpu masks with these functions.

  In particular note that (1 << cpu) just doesn't work with a 64-bit
  cpumask.

  Numerous bits of assembly also had to be adjusted to use e.g. btq instead
  of btl, etc.

* Change __uint32_t declarations that were meant to be cpu masks to use
  cpumask_t (most already have).

  Also change other bits of code which work on cpu masks to be more agnostic.
  For example, poll_cpumask0 and lwp_cpumask.

* 64-bit atomic ops cannot use "iq", they must use "r", because most x86-64
  do NOT have 64-bit immediate value support.

* Rearrange initial kernel memory allocations to start from KvaStart and
  not KERNBASE, because only 2GB of KVM is available after KERNBASE.

  Certain VM allocations with > 32G of ram can exceed 2GB.  For example,
  vm_page_array[].  2GB was not enough.

* Remove numerous mdglobaldata fields that are not used.

* Align CPU_prvspace[] for now.  Eventually it will be moved into a
  mapped area.  Reserve sufficient space at MPPTDI now, but it is
  still unused.

* When pre-allocating kernel page table PD entries calculate the number
  of page table pages at KvaStart and at KERNBASE separately, since
  the KVA space starting at KERNBASE caps out at 2GB.

* Change kmem_init() and vm_page_startup() to not take memory range
  arguments.  Instead the globals (virtual_start and virtual_end) are
  manipualted directly.