Pull more documentation updates from Jonathan Corbet:
 "A handful of late-arriving documentation fixes, plus one Spanish
  translation that has been ready for some time but got applied late"

* tag 'docs-6.4-2' of git://git.lwn.net/linux:
  docs/sp_SP: Add translation of process/adding-syscalls
  CREDITS: Update email address for Mat Martineau
  Documentation: update kernel stack for x86_64
  docs: Remove unnecessary unicode character
  docs: fix "Reviewd" typo
  Documentation: timers: hrtimers: Make hybrid union historical
  docs/admin-guide/mm/ksm.rst fix intraface -> interface typo
  doc:it_IT: fix some typos