Add the Marvell Kirkwood boards we support.

[imp]

Summary

Add support for the dreamplug, guruplug, pogoplug and shivaplug. These
are all SoCs based on the Marvell Kirkwood SoCs. Based, in part, on
notes and really old u-boot from Ian Lepore.

[imp]

Further research suggests pogo plug is not a good thing to add (it would be hard to support)
Maybe add the Seagate FreeAgent DockStar too. The config builds, but no .kwb. I have one of these, but maybe too much of a PITA
Finally, Maybe we just want DreamPlug and call it a day.

[pi]

If shivaplug is written as sheevaplug, shouldn't the port and directory be renamed ?