media: staging: media: imx: imx7-media-csi: Import video device helpers

To prepare for code refactoring, copy the video device helper code used
by this driver verbatim from imx-media-capture. Rename some functions to
avoid name clashes, and leave the legacy ioctls out as they're not used
by the imx7-media-csi driver. No functional change included.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>