Fix make distcheck for Tile

src/Makefile.am was missing util-mpm-ac-tile-small.c which caused
release tarballs for fail to build on Tile-Gx.

passes: make distcheck
Buildbot: https://buildbot.suricata-ids.org/builders/ken-tilera/builds/92
Buildbot-pcal: https://buildbot.suricata-ids.org/builders/ken-tilera-pcap/builds/27