iommu: Split iommu_group_add_device()

iommu: Split iommu_group_add_device()

Move the list_add_tail() for the group_device into the critical region
that immediately follows in __iommu_probe_device(). This avoids one case
of unlocking and immediately re-locking the group->mutex.

Consistently make the caller responsible for setting dev->iommu_group,
prior patches moved this into iommu_init_device(), make the no-driver path
do this in iommu_group_add_device().

This completes making __iommu_group_free_device() and
iommu_group_alloc_device() into pair'd functions.

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/9-v3-328044aa278c+45e49-iommu_probe_jgg@nvidia.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>