pkg-infra: pass --disable-doc if documentation is not enabled

Many configure scripts support an option like --disable-doc, --disable-docs
or --disable-documentation.  Pass all of these to configure.

In addition, not all Xorg packages accept the --disable-xxx. Instead they
look for xmlto and/or fop and build documentation if they exist.  For host
packages, this may lead to build errors because /usr/bin/xmlto uses libxml2
and we set LD_LIBRARY_PATH to point to $(HOST_DIR)/lib, which may contain
a libxml2 as well.  So it's essential to disable xmlto for host packages.

Also some whitespace cleanup.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>