Makefile library merge with onf-make and voltha-lib-go

makefiles/
----------
  o Import standalone makefile directories to checkin smaller parts of a mega patch.
  o Build out directory hierarchy by topic and feature.

makefiles/lint/yaml/
--------------------
  o Pull in logic evolved in repo:voltha-lib-go.
  o Refactoring: support special snowflake targets by repository.
  o ci-management and voltha-lib-go use distinct yamllint.conf files.
  o Separate until there is time to review and consolidate.
  o Added deps for on-demand local install of yamllint.
    - requirements.txt could be used but every build would incur overhead.

Makefile
--------
  o Use latest syntax from repo:onf-make.
  o No need to set path variables, makefiles/include.mk can infer them.
  o Added a help target to explicitly display targets and suggestions.
  o Logic is bundled in libraries and use of 'make help' is not well known.

Change-Id: Id8eba6f914a7bfe9a31637901bd8fb78a387e0c2
diff --git a/makefiles/git/required.mk b/makefiles/git/required.mk
index 29fba88..44f498d 100644
--- a/makefiles/git/required.mk
+++ b/makefiles/git/required.mk
@@ -26,7 +26,7 @@
 # Makefile can also explicitly define the flag to force always loading.
 # -----------------------------------------------------------------------
 $(foreach tgt,$(git-mk-targets),\
-  $(if $(findstring $(tgt),$(MAKECMDGOALS)),$(eval USE_ONF_GIT_MK := true))\
+  $(if $(findstring $(tgt),$(MAKECMDGOALS)),$(eval USE-ONF-GIT-MK := true))\
 )
 
 # [EOF]