media: dt-bindings: adv7180: Introduce 'adv,force-bt656-4' property

Captured NTSC video would be out of sync when using the adv7280 with
the BT.656-4 protocol. Certain registers (0x04, 0x31, 0xE6) need to
be configured properly to ensure BT.656-4 compatibility.

Introduce the 'adv,force-bt656-4' property to allow the ADV7280
behavior to be consistent with the ADV7180, where BT.656-4 timing
is used by default.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>