ARM: mvebu: add Device Tree for the Armada 385 DB board

The Armada 385 DB board is the development board from Marvell for the
Armada 385 SoC. This commit adds a Device Tree description for this
board, which enables the following features:

 * Network interfaces
 * I2C buses
 * SDIO
 * Serial port
 * SPI bus, with a SPI flash
 * PCIe interfaces

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