kernel - SWAP CACHE part 5/many - Change vm_pindex_t to 64 bits on i386

kernel - SWAP CACHE part 5/many - Change vm_pindex_t to 64 bits on i386

* Change vm_pindex_t from unsigned long (32 bits) to __uint64_t (64 bits).
  This change is necessary to support block devices with greater than 16TB
  of storage as well as to support the mmap()ing of HAMMER files larger
  than 16TB.

  Primarily this was done to support block devices greater than 16TB
  since HAMMER volumes are allowed to be up to 4096TB each.  Filesystem
  mounts use VM objects to back block devices.

* On x86_64 vm_pindex_t is already 64 bits but change the typedef from
  unsigned long to __uint64_t to match i386.

* Most conversions to and from vm_pindex_t are to 64 bits anyway so this
  change does not create any performance issues.