dt-bindings: display: renesas: du: Increase indent in output table

The DU output table lists the port combinations for each supported DU
type.  Newer models of R-Car Gen3 platforms have an increased string
length.

Increase the table indentation in preparation for supporting new target
types.
Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>