media: v4l2-subdev: implement VIDIOC_DBG_G_CHIP_INFO ioctl

The VIDIOC_DBG_G/S_REGISTER ioctls imply that VIDIOC_DBG_G_CHIP_INFO is also
present, since without that you cannot use v4l2-dbg.

Just like the implementation in v4l2-ioctl.c this can be implemented in the
core and no drivers need to be modified.

It also makes it possible for v4l2-compliance to properly test the
VIDIOC_DBG_G/S_REGISTER ioctls.

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