Device specific bindings should not allow undefined properties. This is
accomplished in json-schema with 'additionalProperties: false'.

Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>