ARM: dts: Define stdout-path property for Peach boards

The kernel can use as the default console a serial port if is defined
as stdout device in the Device Tree.

This allows a board to be booted without the need of having a console
parameter in the kernel command line.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Kukjin Kim <kgene@kernel.org>