dt-bindings: display: Add missing property types

A couple of display bridge properties are missing a type definition. Add
the types to them.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230613201114.2824626-1-robh@kernel.org


Signed-off-by: Rob Herring <robh@kernel.org>