Change iommu driver to call add_device_to_group trace event. This iommu_group
class event can be enabled to trigger when devices get added to an iommu group.
Trace information includes iommu group id and device name.

Testing:
The following is trace is generated when intel-iommu driver adds devices to
to iommu groups during boot-time during its initialization:

       swapper/0-1     [003] ....     1.854793: add_device_to_group: IOMMU: groupID=0 device=0000:00:00.0
       swapper/0-1     [003] ....     1.854797: add_device_to_group: IOMMU: groupID=1 device=0000:00:02.0
Signed-off-by: NShuah Khan <shuah.kh@samsung.com>
Signed-off-by: NJoerg Roedel <joro@8bytes.org>