* Add squashfs with LZ4 and LZO compression to Barebox
* Add squashfs with LZO compression to U-Boot
* Use "raw" as type for kernel partition which is compatible with ext4
image as well as squashfs.
Note: This does not use squashfs for the kernel but merly adds support
for it. This will allow to downgrade/fallback to the non-squashfs
version. Using squashfs for the kernel partition is implemented in dev
(for release 7).