core/pkg-generic: call MESSAGE when saving package legal-info

core/pkg-generic: call MESSAGE when saving package legal-info

Currently, the per-package legal-info is mostly silent, but we're soon
to add a check for the hashes of the license files.

In that case, and when there is a hash mis-match, we want a user to know
what package had a changed license file.

So, we add a call to MESSAGE to display the package we're currently
saving the legal-info of, like so:

    >>> busybox 1.26.2 Collecting legal info

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Rahul Bedarkar <rahulbedarkar89@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>