powerpc/iommu: Remove iommu_del_device()

Now that power calls iommu_device_register() and populates its groups
using iommu_ops->device_group it should not be calling
iommu_group_remove_device().

The core code owns the groups and all the other related iommu data, it
will clean it up automatically.

Remove the bus notifiers and explicit calls to
iommu_group_remove_device().

Fixes: a9409044 ("powerpc/iommu: Add iommu_ops to report capabilities and allow blocking domains")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/0-v1-1421774b874b+167-ppc_device_group_jgg@nvidia.com