ARM: dts: genmai: Update console parameters

Change the console alias to "serial0", for consistency with other
boards (the first unlabeled serial port is always called "serial0").
This does change the serial console from /dev/ttySC2 to /dev/ttySC0.
Add the serial port config to "chosen/stdout-path", which requires
referring to the port by alias.

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