MPC5200: support setup without FEC

Include FEC specific nodes in ft_cpu_setup only if CONFIG_MPC5xxx_FEC is
defined. Systems without FEC, i.e. no FEC node in DTB, should be possible.

Signed-off-by: Andre Schwarz <andre.schwarz@matrix-vision.de>
Acked-by: Grant Likely <grant.likely@secretlab.ca>