drivers: can: mark CAN-FD data phase timing API as optional

The can_set_timing_data() API function is optional and is not supported by
all CAN controller drivers.

On a board with only either classic CAN or CAN-FD capable controllers the
current behavior is fine, but on boards with a mix of classic CAN and
CAN-FD capable controllers/drivers, calling can_set_timing_data() on a
classic CAN controller will lead to a NULL pointer dereference.

To ensure a proper behavior when calling can_set_timing_data() on classic
CAN controller drivers, change the API wrapper function to return -ENOSYS
if the CAN driver does not implement CAN-FD support.

Note that the data phase timing calculation functions are fine as-is, as
the timing calculations will fail due to minimum/maximum data phase timing
parameters being all zeros for drivers only supporting classic CAN.

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