iommu/ipmmu-vmsa: Convert to generic_single_device_group()

Use the new helper.

This driver is kind of weird since in ARM mode it pretends it has
per-device groups, but ARM64 mode does not.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/6-v1-c869a95191f2+5e8-iommu_single_grp_jgg@nvidia.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>