arm64: dts: meson: g12a: add drive strength for eth pins

With the X96 Max board using an external Gigabit Ethernet PHY,
add the same driver strength to the Ethernet pins as the vendor
tree.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>