ARM: dts: berlin: add the Marvell BG2-Q DMP device tree

Adds initial support for the Marvell BG2-Q DMP. The board has 2GB of
memory, an uart activated and what's initially supported by the Marvell
Armada 1500 pro dtsi.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>