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

In the Linux kernel, the following vulnerability has been resolved: 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.