arm: mvebu: add support for the Armada XP Matrix board

The Armada XP Matrix board is the mother board of a more complex
system. The mother board uses an Armada XP MV78460, 4 serial ports, 2
SATA ports, one Ethernet connection, a PCIe port and a USB port. All
those devices are enabled in the Device Tree added by this patch.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>