[media] v4l2: allow v4l2_subdev_edid to be used with video nodes

Struct v4l2_subdev_edid and the VIDIOC_SUBDEV_G/S_EDID ioctls were
specific for subdevices, but for hardware with a simple video pipeline
you do not need/want to create subdevice nodes to just get/set the EDID.

Move the v4l2_subdev_edid struct to v4l2-common.h and rename as
v4l2_edid. Add the same ioctls to videodev2.h as well, thus allowing
this API to be used with both video nodes and v4l-subdev nodes.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>