ARM: shmobile: genmai dts: Add chosen/stdout-path

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

Remove the now-superfluous "console=" parameter from chosen/bootargs.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>