iommu/arm-smmu: Unregister IOMMU and bus ops on device removal

When removing the SMMU driver, we need to clear any state that we
registered during probe. This includes our bus ops, sysfs entries and
the IOMMU device registered for early firmware probing of masters.

Signed-off-by: Will Deacon <will@kernel.org>
Tested-by: John Garry <john.garry@huawei.com> # smmu v3
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Joerg Roedel <jroedel@suse.de>