ARM: dts: socfgpa: remove ethernet aliases from dtsi

Not all boards use two ethernet devices and/or use them in different
order. As almost all in-tree boards already define their own ethernet
aliases, remove them from the dtsi and add the aliases to the two boards,
that are missing their own definition.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
[dinguyen@kernel.org: rebased to latest dts changes]
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>