msm: kgsl: Add a ftrace event for active_cnt

Add a new ftrace event for watching the rise and fall of active_cnt:

  echo 1 > /sys/kernel/debug/tracing/events/kgsl/kgsl_active_count/enable

This will give you the current active count and the caller of the function:

  kgsl_active_count: d_name=kgsl-3d0 active_cnt=8e9 func=kgsl_ioctl

Change-Id: Ic0dedbadc80019e96ce759d9d4e0ad43bbcfedd2
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>