doc: update Kconfig options to use @option ALIAS

This updates Kconfig options in the Doxygen documentation to use the new
@option ALIAS. There are three categories of fixes:

* Use of `:option:` inside Doxygen headers, which is not valid (this is
  rST syntax!).
* Kconfig options that were just written as plain text and were no
  references were generated.
* Use of `@rst` blocks where the only reason for using them was to have
  Kconfig options resolved.

Signed-off-by: Fabio Utzig <fabio.utzig@nordicsemi.no>