docs: acpi: fix old http link and improve document format

The website:

    http://wiki.minnowboard.org

doesn't exist anymore. The same pages are moved to:

    https://www.elinux.org/Minnowboard



Other improvements concern the introduction of some rst
semantic markup in the document.

Signed-off-by: Flavio Suligoi <f.suligoi@asem.it>
Link: https://lore.kernel.org/r/20200519084128.12756-2-f.suligoi@asem.it


Signed-off-by: Jonathan Corbet <corbet@lwn.net>