drm/msm: Split the a5xx preemption record

The main a5xx preemption record can be marked as privileged to
protect it from user access but the counters storage needs to be
remain unprivileged. Split the buffers and mark the critical memory
as privileged.

Cc: stable@vger.kernel.org
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>