msm: kgsl: Add barriers to GPU fault tolerance memory reads

In GPU fault tolerance When reading from memstore add
memory barriers. This ensures memstore reads are
completed and makes GPU fault tolerance code robust.

Change-Id: Iefb950ae2647eb8ae16bfb9a8d7ee9885636d920
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>