ARM: dts: exynos: Use stdout path property on Arndale Octa board

Replacing bootargs with stdout-path property in chosen node allows using
early console by adding just 'earlycon' parameter to kernel command
line.
Suggested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

arch/arm/boot/dts/exynos5420-arndale-octa.dts

@@ -24,7 +24,7 @@ memory@20000000 {
 	};
 
 	chosen {
-		bootargs = "console=ttySAC3,115200";
+		stdout-path = "serial3:115200n8";
 	};
 
 	firmware@2073000 {