iommu/arm-smmu-v3: Don't unregister on shutdown

iommu/arm-smmu-v3: Don't unregister on shutdown

Similar to SMMUv2, this driver calls iommu_device_unregister() from the
shutdown path, which removes the IOMMU groups with no coordination
whatsoever with their users - shutdown methods are optional in device
drivers. This can lead to NULL pointer dereferences in those drivers'
DMA API calls, or worse.

Instead of calling the full arm_smmu_device_remove() from
arm_smmu_device_shutdown(), let's pick only the relevant function call -
arm_smmu_device_disable() - more or less the reverse of
arm_smmu_device_reset() - and call just that from the shutdown path.

Fixes: 57365a04c921 ("iommu: Move bus setup to IOMMU device registration")
Suggested-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20221215141251.3688780-2-vladimir.oltean@nxp.com
Signed-off-by: Will Deacon <will@kernel.org>