kernel - Refactor suword, fuword, etc. change vmm_guest_sync_addr()

kernel - Refactor suword, fuword, etc.  change vmm_guest_sync_addr()

* Rename the entire family of functions to reduce confusion.

* Change how vmm_guest_sync_addr() works.  Instead of loading one value
  into a target location we exchange the two target locations, with the
  first address using an atomic op.  This will allow the vkernel to
  drop privs and query pte state atomically.