imx8qm-var-som: configure symphony adi,phy-mode-overide to rgmii

The AR8033 and ADIN1300 share the same address, but need different
phy-mode configurations. Use adi,phy-mode-override to override the
phy-mode of the ADIN1300.

Signed-off-by: Nate Drude <nate.d@variscite.com>

arch/arm64/boot/dts/freescale/fsl-imx8qm-var-som-common.dtsi

@@ -731,6 +731,7 @@
 			reg = <5>;
 			at803x,eee-disabled;
 			at803x,vddio-1p8v;
+			adi,phy-mode-override = "rgmii";
 		};
 	};
 };