Add optional build packages for each platform.

The build package contains collateral needed to support the platform but need not be installed in the runtime.
The first use of this package is to export powerpc device trees for each platform (instead of integrating with a particular kernel package).

packages/base/any/templates/platform-config-platform.yml

@@ -11,18 +11,24 @@ prerequisites:
     - "onl-vendor-config-$VENDOR:all"
     - "onl-platform-modules-$BASENAME:$ARCH"
 
+common:
+  version: 1.0.0
+  arch: $ARCH
+  copyright: Copyright 2013, 2014, 2015 Big Switch Networks
+  maintainer: support@bigswitch.com
+  support: opennetworklinux@googlegroups.com
+  changelog: None
+
 packages:
   - name: onl-platform-config-$PLATFORM
     depends: onl-vendor-config-$VENDOR,onl-platform-modules-$BASENAME
-    version: 1.0.0
-    arch: $ARCH
-    copyright: Copyright 2013, 2014, 2015 Big Switch Networks
-    maintainer: support@bigswitch.com
-    support: opennetworklinux@googlegroups.com
     summary: ONL Platform Configuration Package for the $PLATFORM
 
     files:
       src/lib: /lib/platform-config/$PLATFORM/onl
       src/python : ${PY_INSTALL}/onl/platform/
 
-    changelog: Changes
+  - name: onl-platform-build-$PLATFORM
+    summary: ONL Platform Build Package for the $PLATFORM
+    optional-files:
+      builds: $$PKG_INSTALL