[media] adv7604: use presets where possible

Use predefined video timings (prim_mode/vid_std) when available as recommended
by Analog Devices (http://ez.analog.com/message/48267#48267).
Also remove 720p30 support since the ADV7604 can't handle that.
(http://ez.analog.com/message/61488#61488

)

Signed-off-by: Mats Randgaard <matrandg@cisco.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>