Documentation: arm: add URLs to public datasheets for the Marvell Armada XP SoC

Marvell has very recently released a public version of the "Functional
specifications" and "Hardware specifications" datasheets for the
Marvell Armada XP SoC. This allows contributors and developers not
under NDA with Marvell to get more details about this SoC than what
the current kernel code shows, and hopefully allows to improve the
support for this SoC in the mainline kernel, as well as in other
projects.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lkml.kernel.org/r/1406227593-29749-2-git-send-email-thomas.petazzoni@free-electrons.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>