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/src/pdmgen.py b/src/pdmgen.py
index 1ff5c51..6476a95 100755
--- a/src/pdmgen.py
+++ b/src/pdmgen.py
@@ -85,7 +85,7 @@
         help="Generated output file name and path.")
     parser.add_argument(
         '-t', '--template', dest='template',
-        default='generated.mako.cpp',
+        default='generated.mako.hpp',
         help='The top level template to render.')
     parser.add_argument(
         '-p', '--template-path', dest='template_search',