doc: Fix virtualization high level diagram

The current virtualization high level diagram incorrectly shows
the CAM demo deployed on all three Safety Island clusters. This
has been amended to show the CAM demo being deployed on the top
of Saftey Island 1 cluster.

Also added the word 'backported' to .dictionary file.

Signed-off-by: Mubashar Ahmad <mubashar.ahmad@arm.com>