Makefile: install fi_direct_eq.h with HAVE_DIRECT

fi_direct_eq.h should also be installed when HAVE_DIRECT is
enabled.

Signed-off-by: Sayantan Sur <sayantan.sur@intel.com>
Merge pull request #283 from sayantansur/fi-direct-eq

Makefile: install fi_direct_eq.h with HAVE_DIRECT