msm: kgsl: Remove IOMMU units and other legacy code

The concept of IOMMU units harkens back to the 8064 days. The code
was pretty heavily embedded into the infrastructure so it was harder
to remove when the rest of the IOMMUv0 code went to the great
clipboard in the sky. Remove it now and streamline all the interfaces
all the way back to the DT parser.

Change-Id: Ic0dedbad4a33123e37f4b8d272e0421c369e1786
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>