sunxi: Set the /chosen/stdout-path fdt property for sunxi boards

While discussing with some people how to get the Linux kernel to do the
right thing wrt sending output to both the serial console and the
hdmi out / lcd screen when booting on ARM devices, Grant Likely pointed out
that there already is a solution for this.

All we need to do is set the /chosen/stdout-path fdt property, and if no
console= arguments were specified on the kernel commandline the kernel
will honor this and add this device as a console (next to the primary
video output on hdmi).

And u-boot already has support for setting this, all we need to do is
define OF_STDOUT_PATH and then everything will just work ootb, without
people needing to meddle with adding console= arguments in extlinux.conf .

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
Reviewed-by: Tom Rini <trini@ti.com>