msm: mdss: ensure retire fences are signaled during panel off

When turning off command mode panel, if retire fences are still active
and suspend sequence goes through some fences may remain active.
If fences remain active command panel off sequence would stop signaling
vsyncs and would throw off the timeline. To fix this clear the retire
timeline when turning panel off.

Change-Id: I32a5fe0f81b16fa2ef959c7f05e484fb9f9f8598
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>