[media] media: Rename is_media_entity_v4l2_io to is_media_entity_v4l2_video_device

All users of is_media_entity_v4l2_io() (the exynos4-is, omap3isp,
davince_vpfe and omap4iss drivers and the v4l2-mc power management code)
use the function to check whether entities are video_device instances,
either to ensure they can cast the entity to a struct video_device, or
to count the number of video nodes users.

The purpose of the function is thus to identify whether the media entity
instance is an instance of the video_device object, not to check whether
it can perform I/O. Rename it accordingly, we will introduce a more
specific is_media_entity_v4l2_io() check when needed.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>