Add a stdout-path property so that automatic console selection works
in the absence of a "console=" parameter on the kernel command line.

Note that we have to keep the "console=" parameter in chosen/bootargs,
as this DTS is shared between legacy and multi-platform.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>