Uboot sunxi with cubietruck support

Hello,

This is an attempt to add cubietruck uboot to the `uboot-sunxi` package, and eventually add "official" cubietruck support to alarm.

I have made a PR even though it is not ready to be merged, but that lets you look at it and decide how to actually do this.

I see the following issues at this point:

* `uboot-cubieboard2` and `uboot-cubietruck` will obviously conflict if they need to be provided on the same sun7i-rootfs. Renaming the files to e.g. `script.cubieboard2.bin` would solve the conflict but then the user would have to rename the files. Another solution would be to provide a "boot-package" separate from the rest of the rootfs, which would be unique to the type of sun7i device.

* I had to update uboot-sunxi to a version that has cubietruck support, so it could potentially break cubieboard2 since I'm not able to test it on that device.

What do you think, how should this be done?

Source for [cubietruck.fex](https://raw.github.com/cubieboard/cubie_configs/master/sysconfig/linux/cubietruck.fex)