ARM: dts: mvebu: armada-390-db: add support for the Armada 390 DB board

This commit adds description for following features for this board:

- Serial port
- I2C buses
- 16MB SPI-NOR
- USB2.0
- USB3.0
- PCIe interfaces

Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>