media: ivsc: Improve Kconfig help text

Improve the Kconfig help text to convey the ACE is for changing camera
sensor ownership and CSI for configuring the CSI-2 rx and tx.

Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>