feat(build): manage patch version in Makefile

Add VERSION_PATCH macro in Makefile. This will help LTS releases.
While at it, handle VERSION_PATCH macro in .versionrc.js script.

Change-Id: Id3ec359f7768a90ba5c67e35d29736a46eb402b5
Signed-off-by: Yann Gautier <yann.gautier@st.com>
diff --git a/Makefile b/Makefile
index 8e8fba9..6678179 100644
--- a/Makefile
+++ b/Makefile
@@ -9,7 +9,8 @@
 #
 VERSION_MAJOR			:= 2
 VERSION_MINOR			:= 9
-VERSION				:= ${VERSION_MAJOR}.${VERSION_MINOR}
+VERSION_PATCH			:= 0
+VERSION				:= ${VERSION_MAJOR}.${VERSION_MINOR}.${VERSION_PATCH}
 
 # Default goal is build all images
 .DEFAULT_GOAL			:= all