dts: arm: nxp: mcxn94x: add flexcan0 and flexcan1 devicetree nodes

Add devicetree nodes for the two FlexCAN instances present on the
MCXN94x. Only CAN classic is enabled for now due to issues with FlexCAN FD
in relation to the implementation on this SoC.

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>