[media] Add GS1662 driver, a video serializer

You can read datasheet here:
http://www.c-dis.net/media/871/GS1662_Datasheet.pdf



It's a component which supports HD and SD CEA or SDI formats
to SDI output. It's configured through SPI bus.

GS1662 driver is implemented as v4l2 subdev.

Signed-off-by: Charles-Antoine Couret <charles-antoine.couret@nexvision.fr>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>