* Add squashfs with LZ4 and LZO compression to Barebox
* Add squashfs with LZO compression to U-Boot
* Use squashfs for Linux kernel partition
Generate a squashfs image with LZO compression for the Linux kernel
partition. Adjust the boot scripts to be file system independent commands
to boot from squashfs.
The change "Avoid trying to boot non-existing kernel image in failover
case" introduced a broken boot script on Raspberry Pi (when booting from
partition B) and ODROID-XU4.
* Avoid trying to boot non-existing kernel image in fail-over case
The A/B update system automatically switches to the other boot slot when
booting fails. However, in a fresh installation, only boot slot A
exists. If booting fails three times (e.g. if somebody plugs out power
before the slot can be marked as good), then the system switches to boot
slot B which does not contain a kernel image yet. Avoid trying to boot
the non-existing kernel image.
With this change, if slot B is empty U-Boot will restore both slots to 3
attempts and retry booting from slot A on next reboot:
```
Trying to boot slot B, 2 attempts remaining. Loading kernel ...
** Unrecognized filesystem type **
No valid slot found, resetting tries to 3
storing env...
```
Co-authored-by: Pascal Vizeli <pascal.vizeli@syshack.ch>
