msm: kgsl: add per-process memory info to debugfs

Add a file for each process in debugfs named, kgsl/proc/<pid>/mem
which contains information about all memory allocations the process
has made.

Change-Id: Ice3f039d92cc1b1cdb5a6192808441ddfdf8abfb
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>