msm: kgsl: Release hang detect performance counters when not in use

If hang detection is disabled via sysfs or ioctl() release the
performance counters that the hang detection uses so the counters
can be available to other consumers.

CRs-fixed: 533729
Change-Id: Ic0dedbad6998bbdab0f088a45c2bbf6e426e232d
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>