powerpc: ppc4xx: Add defaults for DT based booting to really work

These additional nodes need to be provided to get U-Boot to boot correctly
on the Canyonlands / Glacier board:

- chosen path to the console-uart
- reg-shift set to 0 in the uart device nodes

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>