msm: kgsl: Add accounting for memory mapped in userspace

For proper memory accounting, a key metric is to know how much
memory kgsl allocated for a process and how much of it the process
is actually using. This is done by keeping track of memory in our
vmfault routines. This information is provided via the process
mem file.

Change-Id: I7e3371a708ea5fdade3840b2384b3bc4012ad004
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>