build: General build refactoring

Add vars.mk for variable sharing across makefiles.
Stub and rename example YAML file and template.
  Content to be re-introduced as support is added.
Move generated C++ to a header file.
Add input YAML path option to configure.

Change-Id: Ia06e392e8b120b1e1d8614046064fa432a6f9e18
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/vars.mk b/vars.mk
new file mode 100644
index 0000000..8002262
--- /dev/null
+++ b/vars.mk
@@ -0,0 +1,2 @@
+PDMGEN=${top_srcdir}/src/pdmgen.py
+TEMPLATESEARCH=${top_srcdir}/src/templates