arm64: dts: meson: g12b: odroid-n2: add the Ethernet PHY interrupt line

The interrupt line of the RTL8211F PHY is routed to the GPIOZ_14 pad.
Describe this in the device tree so the PHY framework doesn't have to
poll the PHY status.

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