iommu/ipmmu-vmsa: Use iommu_device_register()/unregister()

Extend the driver to make use of iommu_device_register()/unregister()
functions together with iommu_device_set_ops() and iommu_set_fwnode().

These used to be part of the earlier posted 64-bit ARM (r8a7795) series but
it turns out that these days they are required on 32-bit ARM as well.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Joerg Roedel <jroedel@suse.de>