docs(changelog): changelog for v2.8 release

Change-Id: I1d99ea46ad527993ee786c34a67f94d74470f960
Signed-off-by: Lauren Wehrmeister <lauren.wehrmeister@arm.com>
diff --git a/Makefile b/Makefile
index 4f5ec5d..1ddb7b8 100644
--- a/Makefile
+++ b/Makefile
@@ -8,7 +8,7 @@
 # Trusted Firmware Version
 #
 VERSION_MAJOR			:= 2
-VERSION_MINOR			:= 7
+VERSION_MINOR			:= 8
 VERSION				:= ${VERSION_MAJOR}.${VERSION_MINOR}
 
 # Default goal is build all images