File operations that manipulate the state of the encoder, or video or audio
subdevices or some of the stream flags need to be serialized.  Add the
serilization locks to cx18-alsa in a manner consistent with the locking for
the v4l2 file operations.
Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>