Switch to using devmatch to autoload drivers. Remove usb.conf

as obsolete because devmatch gets its information from the same
place as the genration scripts.

etc/devd/devmatch.conf

@@ -0,0 +1,13 @@
+#
+# $FreeBSD$
+#
+
+#
+# Example devd configuration file for automatically
+# loading what modules we can based on nomatch
+# events.
+#
+# Generic NOMATCH event
+nomatch 100 {
+	action "service devmatch onestart"
+};