makefiles: avoid using vpath for rules files

makefiles: avoid using vpath for rules files

Fixing vpath usage as it has been checking for existance of
generated file also in the $(scrdir) e.g.:

No need to remake target '10-dm.rules.in'; using VPATH name '...'

If the $(srcdir) had been also $(builddir) and contained already
generated rules file, it's been used instead generating new
one.

(See: http://make.mad-scientist.net/papers/how-not-to-use-vpath/)