[media] vb2: add allow_zero_bytesused flag to the vb2_queue struct

[media] vb2: add allow_zero_bytesused flag to the vb2_queue struct

The vb2: fix bytesused == 0 handling (8a75ffb) patch changed the behavior
of __fill_vb2_buffer function, so that if bytesused is 0 it is set to the
size of the buffer. However, bytesused set to 0 is used by older codec
drivers as as indication used to mark the end of stream.

To keep backward compatibility, this patch adds a flag passed to the
vb2_queue_init function - allow_zero_bytesused. If the flag is set upon
initialization of the queue, the videobuf2 keeps the value of bytesused
intact in the OUTPUT queue and passes it to the driver.

Reported-by: Nicolas Dufresne <[email protected]>
Signed-off-by: Kamil Debski <[email protected]>
Acked-by: Hans Verkuil <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>