infra/common: add a new file to list platform names

Instead of repeating the 'platform names' table in multiple documents,
create a new file to list the platform names and remove the table that
lists the platform names in other documents. Let other documents
provide a link to this new document instead.

Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
Change-Id: Iad828bc84674c5ddb59ba00c406e5404feffc586