Remove the DT_CHOSEN_ZEPHYR_CANBUS_LABEL macro and replace it with
DEVICE_DT_GET(DT_CHOSEN(zephyr_canbus)) were possible.
Where both devicetree CAN controllers and Kconfig specified CAN loopback
controllers are supported, the macro is replaced with
DT_LABEL(DT_CHOSEN(zephyr_canbus)) for now.
This is the first pass for removing the requirement for devicetree
labels for CAN controllers.
Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>