Makefile: Update the minor version to indicate 2.4 release

Updated the minor version to '4' to indicate 2.4 release

Change-Id: Ib142fa15baeb43025fae371c7649199b8121c18f
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>

Makefile

@@ -8,7 +8,7 @@
 # Trusted Firmware Version
 #
 VERSION_MAJOR			:= 2
-VERSION_MINOR			:= 3
+VERSION_MINOR			:= 4
 
 # Default goal is build all images
 .DEFAULT_GOAL			:= all