[U-Boot] Mirror to github

Six people have various modifications to u-boot hosted on github. These projects aren't linked to each other.

I just talked to the github people. To fix this the main u-boot repo needs to be pushing a clone of itself to github. This is free to do, just make a git hub account and then set your repo to mirror changes there. Once the mirror is in place, github users can fork from from it. Now github can links these forks to the root repo and not keep six copies.

The linux kernel git tree is already being mirrored at github.

The effect of this is to create a public place where people can work on patches for u-boot.