Let the multiplatform Marzen support boot with the legacy DTS for
Marzen as well as the Marzen reference DTS.

Based on work for the Koelsch board by Laurent Pinchart.

Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>