ARM: dts: imx6ul-kontron-n6x1x-s: Use the standard 'uart-has-rtscts'

The usage of the 'fsl,uart-has-rtscts' property is deprecated.

Use the standard 'uart-has-rtscts' instead.

Cc: Frieder Schrempf <[e-mail]>
Signed-off-by: Fabio Estevam <[e-mail]>
Acked-by: Frieder Schrempf <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

arch/arm/boot/dts/imx6ul-kontron-n6x1x-s.dtsi

···
 &uart3 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_uart3>;
-	fsl,uart-has-rtscts;
+	uart-has-rtscts;
 	status = "okay";
 };