msm: kgsl: Configure the A6XX GPU_BUSY perfcounter

This is needed so that all the GPU blocks contribute to
the GPU BUSY perfcounter. This is needed for proper
performance analysis of the GPU.

Change-Id: I6438b42b378fe766e4e5ae0729a754565a5b0bc7
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>