Documentation: arm: marvell: Fix link to armada_1000_pb.pdf document

File armada_1000_pb.pdf is not available on Marvell website anymore.
So update link to webarchive where is backup copy.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>