ARM: shmobile: alt dts: Drop console= bootargs parameter

Alt is booted from DT, so chosen/stdout-path is
always used, and we can drop the "console=" parameter from chosen/bootargs.

This change has a side-effect of changing the console speed from 38400
to 115200. This is intentional as 115200 is consistently used on
all other shmobile boards.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>