vfio iommu type1: Add find_iommu_group() function

Add find_iommu_group()

Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
Signed-off-by: Neo Jia <cjia@nvidia.com>
Reviewed-by: Jike Song <jike.song@intel.com>
Reviewed-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>