arm64: dts: marvell: espressobin: add ethernet alias

The maker of this board and its variants, stores MAC address in U-Boot
environment. Add alias for bootloader to recognise, to which ethernet
node inject the factory MAC address.

Signed-off-by: Tomasz Maciej Nowak <tmn505@gmail.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>