package/pseudo: add a legacy symlink to emulate fakeroot

In case some post-image script want to call fakeroot, add a symlink to
use pseudo instead.

Reported-by: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>