arm64: dts: marvell: add Ethernet aliases

This patch adds Ethernet aliases in the Marvell Armada 7040 DB, 8040 DB
and 8040 mcbin device trees so that the bootloader setup the MAC
addresses correctly.

Signed-off-by: Yan Markman <ymarkman@marvell.com>
[Antoine: commit message, small fixes]
Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>