Add ethernet0 alias in Nanopi NEO's device tree

This syncs the sun8i-h3-nanopi-neo.dts from the Linux tree, from tag
v5.18-rc1.
The alias is required to enable automatic MAC address generation.

Signed-off-by: Baltazár Radics <baltazar.radics@gmail.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>