util-linux: add back manpages related settings

There was a time that util-linux requres asciidoctor to be there
to have man pages. However, now the tarball ships generated man
pages and will use them. So add back the related settings. Otherwise,
we get the following error when enabling 'doc-pkgs' image feature.

  + update-alternatives --install /usr/share/man/man1/kill.1 kill.1 /usr/share/man/man1/kill.1.procps 200
  update-alternatives: Error: not linking /.../tmp/work/qemux86_64-poky-linux/core-image-minimal/1.0-r0/rootfs/usr/share/man/man1/kill.1 \
  to /usr/share/man/man1/kill.1.procps since /.../tmp/work/qemux86_64-poky-linux/core-image-minimal/1.0-r0/rootfs/usr/share/man/man1/kill.1 exists and is not a link

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>