ExternalCameraHAL: Get old image if taking picture without preview

The root cause is that the dequeue/queue v4l2 buffers is driven by requests.

The potential issue is already noticed and commented in commented in OutputThread::threadLoop().
But setup a sensor thread may need change in architecture.

The patch fix the issue by dropping too old buffers.

Bug: 368087676

Change-Id: I5d6711bc3a73d0bc043b596aee6ce4af4c1841da
Signed-off-by: Fang Hui <hui.fang@nxp.com>