Add ability to force all subpackage version strings to be generated

Originally openpower-pnor-version would only end up rebuilding
subpackages that don't have a version file, even if outdated.
diff --git a/openpower/package/VERSION.readme b/openpower/package/VERSION.readme
index 59fec86..b9b43bb 100644
--- a/openpower/package/VERSION.readme
+++ b/openpower/package/VERSION.readme
@@ -13,12 +13,18 @@
 
     ## Op-build Commands ##
 
-    # Display package version
+    # Display subpackage version
     op-build $(package)-version
 
-    # Force a rebuild of a package version
+    # Display entire pnor version
+    op-build openpower-pnor-version
+
+    # Force a rebuild of a subpackage version
     op-build $(package)-build-version
 
+    # Force a rebuild of all subpackage versions
+    op-build openpower-pnor-build-version-all
+
     ##  Version String (ASCII) ##
 
     General: