ARM: mvebu: Allow MVNETA to be selected with Armada 3700 SoCs

Until now, Armada 3700 SoCs could not enable the mvneta driver, and thus
did not benefit from Ethernet support. Add ARMADA_3700 in the
"depends on" list of the MVNETA Kconfig entry.

Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Stefan Roese <sr@denx.de>