msm: kgsl: Map global pagetable entries after IOMMU attach

Upstream IOMMU driver only supports map after the pagetable
is attached. Change the sequence in GPU driver to match
upstream IOMMU driver requirement.  Panic if we fail to map
global entries.

Change-Id: I1997e11d84b9de545f61bc16fd3d092ba80158f7
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>