zstd shows a good compression rate and is faster than lzo,
also on slow ARM cores.

Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: NMichele Dionisio <michele.dionisio@gmail.com>
[rw: rewrote commit message]
Signed-off-by: NRichard Weinberger <richard@nod.at>