mbedtls: move mbedtls 2.28.5

- Move mbedtls to 2.28.5 version.
- Fix lts builder using 3.x mbedtls rather than 2.28.x
- Update lts2.8-ci-gateway to use lts default refspecs

Change-Id: Ica0f41dbc083a88297279fcd957516142c3c2892
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
diff --git a/tf-a-lts2.8-tftf-gerrit-tforg-l2.yaml b/tf-a-lts2.8-tftf-gerrit-tforg-l2.yaml
index c346223..29eacf9 100644
--- a/tf-a-lts2.8-tftf-gerrit-tforg-l2.yaml
+++ b/tf-a-lts2.8-tftf-gerrit-tforg-l2.yaml
@@ -52,7 +52,7 @@
             default: '+refs/heads/lts-v2.8:refs/remotes/origin/lts-v2.8'
         - string:
             name: MBEDTLS_URL
-            default: 'https://github.com/Mbed-TLS/mbedtls/archive/mbedtls-2.28.1.tar.gz'
+            default: 'https://github.com/Mbed-TLS/mbedtls/archive/mbedtls-2.28.5.tar.gz'
         - string:
             name: SHARE_FOLDER
             default: '/srv/shared/${JOB_NAME}/${BUILD_NUMBER}'