kernel - pmap (i386) - Reduce kmem use for foreign pmap mapping

kernel - pmap (i386) - Reduce kmem use for foreign pmap mapping

* We've been having problems running out of KVA on i386 systems due to
  numerous reasons.  KVA use by the kernel is just too tight.

* Reserve space for foreign pmap page table mappings on a cpu-by-cpu basis
  instead of for SMP_MAXCPU.  This reduces KVM use from 68MB to (ncpu*4MB).
  Use the APT entry for cpu0 and use kmem_alloc_nofault() for the APs.

  This frees up 52MB of KVA which doesn't sound like a lot but actually
  is.

* Add an alignment argument to kmem_alloc_nofault() and vm_map_find().

* vm_map_findspace() already had an alignment argument, but adjust the
  value passed to be at least PAGE_SIZE (this has no operational effect
  but is more correct).