Since commit

| 1f923440 ("dt-bindings: can: add can-controller.yaml")

there is a common CAN controller binding. Add this to the ctucanfd
binding.

Cc: Ondrej Ille <ondrej.ille@gmail.com>
Acked-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>