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

Testing:
Added trace calls to iommu_prepare_identity_map() for testing some of the
conditions that are hard to trigger. Here is the trace from the testing:

       swapper/0-1     [003] ....     1.854101: remove_device_from_group: IOMMU: groupID=0 device=0000:00:02.0
Signed-off-by: NShuah Khan <shuah.kh@samsung.com>
Signed-off-by: NJoerg Roedel <joro@8bytes.org>