msm: kgsl: Make global memory statistics atomic

If you run aggressive memory operations long enough, eventually you
will notice that the KGSL memory statistics will explode up into the
3G range. This is a race condition on the statistics math which ends up
going negative in certain cases.  Turning the statistics variables into
atomics should solve the problem once and for all. ONCE AND FOR ALL.

Change-Id: Ic0dedbad61762d667550c22190c4f9d0b453829b
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>