media: dt-bindings: media: video-interfaces: Add new bus-type

No properly bus-type for DPI video bus, add bus-type 7 for it.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Xin Ji <xji@analogixsemi.com>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>