Bump version to 2.28.0

Executed ./scripts/bump_version.sh --version 2.28.0 --so-tls 14

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/Makefile b/library/Makefile
index 71a1bb0..54b0651 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -39,7 +39,7 @@
 endif
 endif
 
-SOEXT_TLS=so.13
+SOEXT_TLS=so.14
 SOEXT_X509=so.1
 SOEXT_CRYPTO=so.7