ARM: dts: berlin: Enable ethernet on Sony NSZ-GS7

Marvell Berlin BG2 based Sony NSZ-GS7 has one ethernet controller
connected to rear RJ45 jack. Enable it by default.

Tested-by: Antoine Ténart <antoine.tenart@free-electrons.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>