[media] media: videobuf2: Prepare to divide videobuf2

[media] media: videobuf2: Prepare to divide videobuf2

Prepare to divide videobuf2
- Separate vb2 trace events from v4l2 trace event.
- Make wrapper functions that will move to v4l2-side.
- Make vb2_core_* functions that will remain in core-side.
- Add a callback function table for buffer operation which makes vb2-core
  to be able to invoke a v4l2-side functions.
- Rename internal functions as vb2_*.

Signed-off-by: Junghak Sung <[email protected]>
Signed-off-by: Geunyoung Kim <[email protected]>
Acked-by: Seung-Woo Kim <[email protected]>
Acked-by: Inki Dae <[email protected]>
Signed-off-by: Hans Verkuil <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>