nios2: add earlycon support to 3c120 devboard DTS

Allow earlycon to be used on the JTAG UART present in the 3c120 GHRD.
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

arch/nios2/boot/dts/3c120_devboard.dts

@@ -159,6 +159,7 @@ partition@800000 {
 	};
 
 	chosen {
-		bootargs = "debug console=ttyJ0,115200";
+		bootargs = "debug earlycon console=ttyJ0,115200";
+		stdout-path = &jtag_uart;
 	};
 };