audit: update legal info

audit: update legal info

Programs are released under GPLv2+. README file says libraries
libaudit.* and libauparse.* are released under LGPL but there are two
files auparse/strsplit.c and lib/strsplit.c which are released under
GPLv2+ which makes both libraries GPL. Until we review situation with
upstream, we simply mention "unclear (libraries)".

Signed-off-by: Rahul Bedarkar <rahul.bedarkar@imgtec.com>
[Thomas: add "unclear (libraries)" as suggested by Arnout.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>