msm: iommu: Remove the vcap iommu from 8960ab

There is no vcap iommu in the 8960ab platform.
Also, a cleaner separation between platforms is
obtained by re-organizing the gfx3d and vcap
structures by device block instead of by msm.

Change-Id: I9dbfceebe67d44c4ee65e960873e2f9a1811f913
Signed-off-by: Joel King <joelking@codeaurora.org>