media: coda: normalise debug output

Consistently add the context index to debug output, which otherwise is
impossible to make sense of when two contexts are running concurrently.
For this purpose, add a convenience macro coda_dbg(). Use the function
name with the coda_ prefix stripped as keyword where applicable, and
consistently use vid-out and vid-cap names for the queues. Add sequence
counters to the decoder job finished message and correctly indicate B
frames. Add a start streaming message to complement the stop streaming
message and a start encoding message to complement the existing start
decoding message.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>