dt-bindings: can: m_can: change from additional- to unevaluatedProperties

This allows the usage of properties like termination-gpios and
termination-ohms, which are specified in can-controller.yaml
but were previously not usable due to additionalProperties: false.

Signed-off-by: Leonard Göhrs <l.goehrs@pengutronix.de>
Suggested-by: Rob Herring <robh@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Chandrasekar Ramakrishnan <rcsekar@samsung.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>