msm: kgsl: Limit the maximum number of contexts

Enforce a limit of 200 contexts per process. This is done so
that a process cannot use up all the available contexts and
prevent other processes from starving.

Change-Id: I6eda123128381a213315561cd42335e0944f1f55
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>