[U-Boot] LL TEMAC V6 refactored

[Stephan Linz]

@Michal: please, can you test this code on Xilinx PPC4xx platforms
and acknowledge the results? I have no access to a ml405 and ml507.

Note: To use the driver on Microblaze, you will need additional
platform patches by Michal Simek:
  - http://patchwork.ozlabs.org/patch/112535/
  - http://patchwork.ozlabs.org/patch/112534/
  - http://patchwork.ozlabs.org/patch/112532/

I will collect all related patches on a public bundle:
  - http://patchwork.ozlabs.org/bundle/rexut/net-ll_temac/

br,
Stephan