msm: kgsl: Reset busy data after soft reset

GPU perfcounters gets reset after a soft reset. Currently
GPU busy stats is using previous values after a soft reset.
This might lead to invalid GPU busy calculations. Start GPU
stats from the scratch after a soft reset to get valid GPU
busy calculations.

Change-Id: Ia38c18ad59f438d724ff4710ee2b350853b3810d
Signed-off-by: Abhilash Kumar <krabhi@codeaurora.org>