arm64: tegra: Add missing #phy-cells property on Jetson TX2

PHYs need to have a #phy-cells property that defines how many cells are
required in their specifier. The standard Ethernet PHY doesn't require
a specifier, so set its #phy-cells to 0.

Signed-off-by: Thierry Reding <treding@nvidia.com>

arch/arm64/boot/dts/nvidia/tegra186-p3310.dtsi

@@ -50,6 +50,8 @@ phy: phy@0 {
 				interrupt-parent = <&gpio>;
 				interrupts = <TEGRA186_MAIN_GPIO(M, 5)
 					      IRQ_TYPE_LEVEL_LOW>;
+
+				#phy-cells = <0>;
 			};
 		};
 	};