msm: kgsl: Re-run the events handler when inflight goes to zero

The event code is sensitive to race conditions with the GPU. We just
can't spend all day the event loops waiting for timestamp to expire.
The dispatcher loop on the other hand is far less sensitive to the
race with the GPU so we have a very good idea when the GPU is idle.

When inflight goes to zero re-run re-queue the event handler to catch
any stragglers.

CRs-fixed: 551825
Change-Id: Ic0dedbad9d02fca89724bf791d9c7212712a8014
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>