msm: clean up iommu contexts and domains

Group the iommu context together in a logical manner (by subsystem)
to make the code easier to read. Also correct some errors with the
initial pass of context and domains (missing video context and
ijpeg+jpegd domains incorrectly marked as video)

Change-Id: I29064063e1117209beea9fbad044389cc246ed39
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>