bionic-amd64-tf-m-build: Switch to use armclang's from S3 bucket

Arm Clang toolchains are no longer accessible via straight HTTP requests.
Instead, they are mirrored to an S3 bucket, files from which are made
available to build.sh, which in turn makes them available to Dockerfile.

This is similar to changes previously made to TF-A images.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: Iebf0b1089d1963bac8aa8b49621540741762183f
diff --git a/bionic-amd64-tf-m-build/Dockerfile b/bionic-amd64-tf-m-build/Dockerfile
index c04a4ce..c330118 100644
--- a/bionic-amd64-tf-m-build/Dockerfile
+++ b/bionic-amd64-tf-m-build/Dockerfile
@@ -65,6 +65,9 @@
 COPY tf-*.install /tmp/
 COPY setup-sshd /usr/sbin/setup-sshd
 
+# Copy armclang toolchains
+COPY DS500-BN-00026-r5p0-15rel0.tar.gz /tmp/
+
 RUN set -ex ;\
     echo 'locales locales/locales_to_be_generated multiselect C.UTF-8 UTF-8, en_US.UTF-8 UTF-8 ' | debconf-set-selections ;\
     echo 'locales locales/default_environment_locale select en_US.UTF-8' | debconf-set-selections ;\