Update release minor version string

Change-Id: I67382383fc9d18ab57c7e51f793145cb14c6fec5
Signed-off-by: Sathees Balya <sathees.balya@arm.com>

Makefile

@@ -8,7 +8,7 @@
 # Trusted Firmware Version
 #
 VERSION_MAJOR			:= 1
-VERSION_MINOR			:= 5
+VERSION_MINOR			:= 6
 
 # Default goal is build all images
 .DEFAULT_GOAL			:= all