msm: vidc: fix memory leak issue in dynamic buffer mode

While flushing output buffers held in v4l2 video
driver, i.e, with ref count equal to 2, the driver
was freeing the binfo structure. This would leak
the mapped output buffer memory. By avoiding
freeing of the binfo structure, the driver waits
for the release reference event from the firmware
to free and unmap the output buffer. Also move
initialization of dequeued flag for buffers to be
held in driver, till the time we queue this buffer
to firmware. By not doing so, the video driver can
enter a race condition, whereby, a output buffer could
be unmapped and freed before v4l2 client has called
dequeue on the buffer.

Change-Id: Ic95f13b9f4426574012539a76c0b87bedb8e805a
Signed-off-by: Arun Menon <avmenon@codeaurora.org>