Bump __FreeBSD_version for r269398, since it changes the
internal interfaces between the NFS related modules.
This is a direct commit to stable/10.
Add an UPDATING entry for the __FreeBSD_version bump related
to r269398.
MFC r258436: Refactor amd64 startup SMAP parsing

  Extracted from the projects/uefi branch, this change is a reasonable
  cleanup and will reduce the diffs to review when bringing in the
  UEFI work.