playbin2/playsink: Decide if A/V caps are raw only inside playsink

playbin2/playsink: Decide if A/V caps are raw only inside playsink

Before playbin2 would use different selectors for raw audio and
compressed audio (and the same for video) and used different
pads from playsink. This made the involved logic much more
complex and was not implemented completely in playsink, which
made it impossible to support files with a compressed and
uncompressed stream that is support by the sink.

playbin2 handles raw/non-raw streams the same now and the
decision is left to playsink, which now can also handle
caps changes from raw to non-raw and the other way around.

Fixes bug #632788.