arm64: dts: meson: g12a: x96-max: add the Ethernet PHY interrupt line

X96 Max has the PHY reset and interrupt lines are identical to the
Odroid-N2:
- GPIOZ_14 is the interrupt on X96 Max
- GPIOZ_15 is the reset line on X96 Max

Add GPIOZ_14 as PHY interrupt line on the X96 Max so we don't have to
poll for the PHY status.

Suggested-by: Neil Armstrong <narmstrong@baylibre.com>
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>