Automatically update FP5 u-boot image

[chrisduerr]

Currently we're shipping a Tauchgang u-boot image and the boot partition image as static files on catacomb.org. These need to be manually updated and especially the boot partition image risks going out of date with the shipped root images.

To ensure these are always up to date, they should be automatically updated from the build server.

[chrisduerr]

The easier and probably better solution would be to just tar up the two images. That way it can still be distributed as a single image, but uploading and file management are just as easy.

This only applies for the boot filesystem image, the u-boot image still needs an automated solution.