msm: kgsl: Locate index of recovery during initialization

When a hang happens locate the index in ringbuffer from where replay
of recovery needs to be re-tried during initialization of recevery.
If the hang detection is false then hang reported by postmortem and
snapshot may be different, but recovery will always start from the
index obtained during initialization. Also, this allows us to capture
data into the snapshot that is in line with the point from where
recovery occurred.

Change-Id: Ie3877f0c81dad2ede888db7cb7d3ff13e2761763
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>