Add tf-a-builder/lts-builders.sh for LTS build jobs

Add a new builder script, lts-builders.sh
to freeze the armclang on v6.18 for all LTS build jobs

[1]: https://linaro.atlassian.net/browse/TFC-721

Change-Id: Ib7514f7c07eb621aff1c4fa06b9d7fea6990b1b7
Signed-off-by: Arthur She <arthur.she@linaro.org>
diff --git a/tf-a-lts2.10-builder.yaml b/tf-a-lts2.10-builder.yaml
index ac7555a..a91ac61 100644
--- a/tf-a-lts2.10-builder.yaml
+++ b/tf-a-lts2.10-builder.yaml
@@ -130,7 +130,7 @@
         - shell:
             !include-raw: scripts/clone.sh
         - shell:
-            !include-raw: tf-a-builder/builders.sh
+            !include-raw: tf-a-builder/lts-builders.sh
         - inject:
             properties-file: artefacts/env
         - shell: |