For those who might want to use the mainline Kernel with device tree for the L138 and/or the AM1808, here is a tip for getting the MAC address to appear correctly:

loadfdt=load ${devtype} ${bootpart} ${fdtaddr} ${bootdir}/${fdtfile}; fdt addr ${fileaddr} ${filesize};
 fdt resize; fdt set /soc@1c00000/ethernet@220000 local-mac-address "[00 08 ee 04 32 8e]"  

Just replace the contents inside the brackets with the correct MAC address.This will modify the contents of the device tree and push the updated MAC address to the kernel. 

eth0      Link encap:Ethernet  HWaddr 00:08:EE:04:32:8E                                                
          inet6 addr: fe80::208:eeff:fe04:328e/64 Scope:Link                                           
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1                                           
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0                                           
          TX packets:12 errors:0 dropped:0 overruns:0 carrier:0                                        
          collisions:0 txqueuelen:1000                                                                 
          RX bytes:0 (0.0 B)  TX bytes:1480 (1.4 KiB)                                                  
          Interrupt:33             

Notice the HWAddr matches the MAC address passed in the device tree.

adam