psuedo: Add tracking of linked files for fds

Where files are link()'d and one is unlink()'d, pseudo's fd mappings
can become confused. Add a patch to try and improve this for the common
usecases we see.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 9ce621fa)
Signed-off-by: Steve Sakoman <steve@sakoman.com>