msm: kgsl: Move global pagetable entries to the IOMMU driver

Global pagetable entries are exclusively for IOMMU and per-process
pagetables.  Move all the code out of the generic driver and into
the IOMMU driver and clean up a bunch of stuff along the way.

Change-Id: Ic0dedbadbb368bb2a289ba4393f729d7e6066a17
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>