mpc83xx: write MAC address to mac-address and local-mac-address

Some device trees have a mac-address property, some have local-mac-address,
and some have both.  To support all of these device trees, this patch
updates ftp_cpu_setup() to write the MAC address to mac-address if it exists.
This function already updates local-mac-address.

Signed-off-by: Timur Tabi <timur@freescale.com>