arm: octeontx2: Add dtsi/dts files for Octeon TX2 CN913x DB

This patch adds the dtsi/dts files needed to support the Marvell
Octeon TX2 CN913x DB. This is only the base port with not all
interfaces supported fully.

Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>