[media] cobalt: add new driver

The cobalt device is a PCIe card with 4 HDMI inputs (adv7604) and a
connector that can be used to hook up an adv7511 transmitter or an
adv7842 receiver daughterboard.

This device is used within Cisco but is sadly not available outside
of Cisco. Nevertheless it is a very interesting driver that can serve
as an example of how to support HDMI hardware and how to use the popular
adv devices.

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