You could store MAC address in software or in U-boot environment configuration, which is stored in the same memory as u-boot.
Under u-boot prompt, you could configure MAC addresses as the following.
=> setenv eth1addr 00:04:9F:06:04:49
=> setenv eth2addr 00:04:9F:06:04:4A
=> setenv eth3addr 00:04:9F:06:04:4B
=> setenv eth4addr 00:04:9F:06:04:4C
=> setenv eth5addr 00:04:9F:06:04:4D
=> setenv eth6addr 00:04:9F:06:04:4E
=> setenv eth7addr 00:04:9F:06:04:4E
=>setenv ethaddr 00:04:9F:06:04:48
=> saveenv