iommu/omap: Remove platform data da_start and da_end fields

The fields were used by the now gone omap-iovmm driver. They're not used
anymore, remove them.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>