arm64: mvebu: Add support for the DB-88F8040 Armada 8k devel board

This patch adds the necessary files to support the Marvell Armada 8k
devel board. Most board specfic files are shared with the Armada 7k
boards under the name "armada-8k*". So only minimal changes are
necessary to add this basic board support (except the DT files of
course).

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Nadav Haklai <nadavh@marvell.com>
Cc: Neta Zur Hershkovits <neta@marvell.com>
Cc: Kostya Porotchkin <kostap@marvell.com>
Cc: Omri Itach <omrii@marvell.com>
Cc: Igal Liberman <igall@marvell.com>
Cc: Haim Boot <hayim@marvell.com>
Cc: Hanna Hawa <hannah@marvell.com>