media: dt: bindings: Explicitly specify bus type

In the vast majority of cases the bus type is known to the driver(s)
since a receiver or transmitter can only support a single one. There
are cases however where different options are possible, or the bus type
cannot be automatically detected.

The existing V4L2 OF support tries to figure out the bus type and
parse the bus parameters based on that. This does not scale too well
as there are multiple serial busses that share common properties.

Some hardware also supports multiple types of busses on the same
interfaces.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>
Reviewed-by: Sebastian Reichel <sre@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>