[media] davinci: drop unused control callbacks

These callbacks are no longer used since the davinci drivers use the
control framework.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: Prabhakar Lad <prabhakar.csengg@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>