msm: iommu: Add device name to drvdata

Add the human readable name of the iommu device to drvdata.
This makes debugging iommu page faults much easier since
the faulting device name is immediately present. The
context where the fault occured can the be derived from
existing information.

Change-Id: I63b6f05dea155e40f1176f2bebb5eb3cee69a412
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>