[media] vimc: common: Add vimc_pipeline_s_stream helper

Move the vimc_cap_pipeline_s_stream from the vimc-cap.c to vimc-common.c
as this core will be reused by other subdevices to activate the stream
in their directly connected nodes

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>