msm: kgsl: Move global event groups

The iommu event group is more suited to be part of the iommu
structure and the global events are actually better suited for
rb structure. Move these event groups to more appropriate location.

Change-Id: I138a5779bbe6a7f55cccc86ddcdda3a4dee051ed
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>