[U-Boot] U-boot level MPC8548 Ethernet internal/External Loop backtesting

[Swarthout Edward L-SWARTHOU]

From: Ajeesh Kumar
> 
> We have a custom board with MPC8548E processor, please help 
> me in suggesting/sharing Ethernet Internal/External Loopback 
> testing code piece. Also any Phy level loop back too.

If you have a typical phy and this commit applied, you can use the mii 
command to put the phy in loopback and ping your own ip.

Something like:
=> mii r 0 0
1040
=> mii w 0 0 5040  # set bit 14
=> ping $ipaddr

http://git.denx.de/?p=u-boot.git;a=commit;h=83853178bd36bca6f0f8f1331476
620c84a587fc

-Ed