arm64: dts: meson: u200: add internal network

The u200 is the main mother board for the S905D2. It can provide
both the internal and external network. However, by default the
resistance required for the external RGMII bus are not fitted, so
enable the internal PHY.

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