Pull more documentation updates from Jonathan Corbet:
 "Connect the newly RST-formatted documentation to the rest; this had to
  wait until the input pull was done. There's also a few small fixes
  that wandered in"

* tag 'docs-4.12-2' of git://git.lwn.net/linux:
  doc: replace FTP URL to kernel.org with HTTPS one
  docs: update references to the device io book
  Documentation: earlycon: fix Marvell Armada 3700 UART name
  docs-rst: add input docs at main index and use kernel-figure