volume_id: add LittleFS detection

volume_id: add LittleFS detection

Add support for LittleFS to blkid. Not included if FEATURE_BLKID_TYPE
is not selected (neither UUID nor label).

LittleFS is a small fail-safe filesystem designed for embedded
systems. It has strong copy-on-write guarantees and storage on disk
is always kept in a valid state. It also provides a form of dynamic
wear levelling for systems that can not fit a full flash translation
layer. (https://github.com/geky/littlefs)

ARM has introduced it in its Mbed OS 5.7, so it starts to gain focus.
(https://os.mbed.com/blog/entry/littlefs-high-integrity-embedded-fs/)

function                                             old     new   delta
volume_id_probe_lfs                                    -      62     +62
fs1                                                   20      24      +4

Signed-off-by: Sven-Göran Bergh <sgb@systemaxion.se>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>