msm: kgsl: Keep a list of perfcounters per file descriptor

We need a list of perfcounters for each kgsl file descriptor, in
order to gracefully release any perfcounter allocated using that fd
in the event that the process dies unexpectedly or doesn't release
the perfcounters properly. This prevents possible leakage of
perfcounters referenced by a process.

Change-Id: Ib443282f26a0cbdad656fa0f82fb62c6de871fb0
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>