tf-a-lts2.8-tftf-gerrit-tforg-l1,2: Set MBEDTLS_URL to 2.28.1

As required for the LTS branch.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: If262d22e1af3b94f8df62d2e352b567e86185307
diff --git a/tf-a-lts2.8-tftf-gerrit-tforg-l2.yaml b/tf-a-lts2.8-tftf-gerrit-tforg-l2.yaml
index 6ee630c..c369ae3 100644
--- a/tf-a-lts2.8-tftf-gerrit-tforg-l2.yaml
+++ b/tf-a-lts2.8-tftf-gerrit-tforg-l2.yaml
@@ -43,6 +43,9 @@
             name: CI_REFSPEC
             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'
+        - string:
             name: SHARE_FOLDER
             default: '/srv/shared/${JOB_NAME}/${BUILD_NUMBER}'
             description: 'Folder containing shared repositories for downstream pipeline jobs'