[media] v4l2: add new VIDIOC_DBG_G_CHIP_NAME ioctl

Simplify the debugging ioctls by creating the VIDIOC_DBG_G_CHIP_NAME ioctl.
This will eventually replace VIDIOC_DBG_G_CHIP_IDENT. Chip matching is done
by the name or index of subdevices or an index to a bridge chip. Most of this
can all be done automatically, so most drivers just need to provide get/set
register ops.
In particular, it is now possible to get/set subdev registers without
requiring assistance of the bridge driver.

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