media: imx219: Advertise embedded data node on media pad 1

This commit updates the imx219 driver to adverise support for embedded
data streams.  This can then be used by the bcm2835-unicam driver, which
has recently been updated to expose the embedded data stream to
userland.

The imx219 sensor subdevice overloads the media pad to differentiate
between image stream (pad 0) and embedded data stream (pad 1) when
performing the v4l2_subdev_pad_ops functions.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>