* 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.
* Remove CONFIG_CLOCKSOURCE_EFI configuration
It seems to cause messages like this on some machines:
EFI Event timer too slow freq = 100 Hz
The Barebox efi_defconfig configurationd doesn't enable it either.
Disable it by default as well.
* Enable CONFIG_CMD_ECHO_E to fix menutree
It seems that menutree needs CONFIG_CMD_ECHO_E to properly display the
boot menu.
Also enable other useful commands such as edit or reset.
* Bump Barebox to 2021.05.0
