msm: kgsl: Allocate the profile shared buffer once when enabled

No need to continuously allocate/free the shared buffer for profiling.
Only allocate this buffer once when profiling is enabled (as to not
waste space if not enabled).  The buffer is now only freed when
profiling is closed.

Change-Id: I1da53a133badede1b35eb8f1d48bdafceb3959ff
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>