iommu/omap: Drop legacy-style device support

All the supported boards that have OMAP IOMMU devices do support
DT boot only now. So, drop the support for the non-DT legacy-style
devices from the OMAP IOMMU driver. Couple of the fields from the
iommu platform data would no longer be required, so they have also
been cleaned up. The IOMMU platform data is still needed though for
performing reset management properly in a multi-arch environment.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>