[media] vimc: Move common code from the core

Remove helper functions from vimc-core and add it in vimc-common to
clean up the core.

Signed-off-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>