imx: kontron-sl-mx8mm: Remove deprecated phy-mode property

This was previously needed, but U-Boot is now capable of parsing
the new "phy-connection-type" property that is already used in
the main devicetree.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Fabio Estevam <festevam@denx.de>

arch/arm/dts/imx8mm-kontron-n801x-u-boot.dtsi

@@ -25,10 +25,6 @@
 	};
 };
 
-&fec1 {
-	phy-mode = "rgmii-rxid";
-};
-
 &i2c1 {
 	u-boot,dm-spl;
 	u-boot,dm-pre-reloc;