drm/msm/sde: move release/retire fence signal after vsync/ppdone

Move release/retire fences to be signalled in the event thread
queued after vsync/pingpong done interrupt. Also, set accurate
timestamp to the fences struct. Below would be the timelines for
fence signalling.
- Video Mode
    - Signal retire fence - after vsync
    - Signal release fence - after vsync
- Cmd Mode
    - Signal retire fence - after vsync
    - Signal release fence - after pingpong done
- Writeback
    - Signal retire fence - after writeback done
    - Signal release fence - after writeback done

Change-Id: Iba035826e9603dcb77ab71e5560f47f99c6a2dba
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>