ARM: shmobile: marzen: Board specific serial port order

Convert Marzen to use board-specific serial0 and serial1 instead
of the older shared SoC-specific SCIF index.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>