[media] v4l2: drop V4L2_CHIP_MATCH_SUBDEV_NAME

After using the new VIDIOC_DBG_G_CHIP_NAME ioctl I realized that the matching
by name possibility is useless. Just drop it and rename MATCH_SUBDEV_IDX to
just MATCH_SUBDEV.
The v4l2-dbg utility is much better placed to match by name by just enumerating
all bridge and subdev devices until chip_name.name matches.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>