arm: mvebu: use recently introduced uart label for stdout-path

Now that labels for uartX are available in Marvell Armada .dtsi files,
this patch replaces the "/soc/internal-regs/serial@12000" found in
armada-xp-lenovo-ix4-300d.dts file for stdout-path property by the more
concise &uart0.

Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Suggested-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Arnaud Ebalard <arno@natisbad.org>
Link: https://lkml.kernel.org/r/d1a883510e01f7f212a385e826dccbef903fae42.1416613429.git.arno@natisbad.org


Signed-off-by: Jason Cooper <jason@lakedaemon.net>