arm64: dts: meson: g12a: add ethernet mac controller

Add the synopsys ethernet mac controller embedded in the g12a SoC family.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>