msm: kgsl: Save/restore performance counters across GPU power collapse

Physical performance counters are reset on GPU power collapse.
Save the values of the performance counters when the GPU goes to
power collapse and restore them on restart.

Change-Id: I63bec7b20e7fe516bbac4901cac0af3a1c1f4959
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>