msm: kgsl: store process comm name in kgsl_process_private

Now that contexts keep a reference on their owning
kgsl_process_private, look up pid and process from there.
If the process is exiting while hanging the GPU, the
process name might not be available anymore by the time
we make the snapshot.

Change-Id: If05ae2096dd7d25bfe9931e949759e11ba3cd262
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>