eudev: disable manpages

If host-libxslt or some libxslt is around (xsltproc) eudev will try to
build manpages with it. Problem is docbook DTDs might not be around and
things will break. We want no manpages anyway. Fixes:
http://autobuild.buildroot.net/results/c4e/c4e920b16c57e79df979f00cceaea7c0483f043c/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>