mkdeb: use compression level 0

This requires calling dpkg-deb directly and pass it -z0.

It reduces the time to run the mkdeb script from 14 seconds to 3
seconds on my workstation with SSD, from 87s to 15s on a machine
with HDD. The deb file grows from 49M to 58M.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/misc/mkdeb

@@ -59,7 +59,7 @@ find deb/etc -type f -printf /etc/%P\\n >deb/DEBIAN/conffiles
 
 # Package it up
 chown -R root:root deb
-dpkg --build deb xen-upstream-$version.deb
+dpkg-deb --build -z0 deb xen-upstream-$version.deb
 
 # Tidy up after ourselves
 rm -rf deb