iommu: Keep a list of allocated groups in __iommu_probe_device()

This is needed to defer default_domain allocation for new IOMMU groups
until all devices have been added to the group.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20200429133712.31431-10-joro@8bytes.org


Signed-off-by: Joerg Roedel <jroedel@suse.de>