This moves the current documentation in files specific to each
platform family. PowerNV machine is updated, the other machines need
to be done.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20210222133956.156001-1-clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
[dwg: Trivial capitalization fix]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>