V4L/DVB (9530): Add new pixel format VYUY 16 bits wide.

There were already 3 YUV formats defined :
 - YUYV
 - YVYU
 - UYVY
The only left combination is VYUY, which is added in this
patch.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>