YOVEUR: Enable engine by default.

We ship this with 1.7.0 according to our release plans, thus it should really
be enabled by default.

(cherry picked from commit d1157af)

engines/voyeur/configure.engine

@@ -1,4 +1,4 @@
 
 # This file is included from the main "configure" script
 # add_engine [name] [desc] [build-by-default] [subengines] [base games] [deps]
-add_engine voyeur "Voyeur" no
+add_engine voyeur "Voyeur" yes