media: cedrus: Add format reset helpers

By re-arranging try format handlers and set out format handler, we can
easily implement reset out/cap format helpers.

There is only one subtle, but important functional change. Capture
pixel format will be reset each time output format is set. This is
actually expected behaviour per stateless decoder API.

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>