omap3isp: Remove iommu_group related code

The OMAP IOMMU driver has added the support for IOMMU groups internally,
and the ISP device is automatically linked to the appropriate IOMMU group.
So, remove the explicit function calls that creates/deletes an iommu_group
and adds the ISP device to this group.

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>